UBC Theses and Dissertations

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UBC Theses and Dissertations

An evaluation of IMS/VS Miguel, Jose P. 1982

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AN EVALUATION OF IMS/VS by JOSE P. MIGUEL B.Sc U n i v . de I n g e n i e r i a Lima, Peru 1975 A THESIS SUBMITTED IN PARTIAL FULFILLMENT THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES Department of Computer S c i e n c e We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o t. r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA December 1982 Q Jose P. M i g u e l , 1982 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. I t i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of Computer .Science  The University of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date January 14, 1983 DE-6 (.3/81) i i ABSTRACT T h i s t h e s i s p r e s e n t s an e v a l u a t i o n of the f a c i l i t i e s a v a i l a b l e under IBM's IMS/VS Data Base Management Systems. Chapter 1 d e s c r i b e s the IMS/VS main f a c i l i t i e s , and i s an i n t r o d u c t i o n t o c h a p t e r 2. Chapter 2 p r e s e n t s sumaries of e v a l u a t i o n of IMS/VS c h a r a c t e r i s t i c s . These c h a r a c t e r i s t i c s a r e grouped i n c a t e g o r i e s as su g g e s t e d by the Data Base D i s c u s s i o n Group (DBDG) of UBC i n s e t t i n g g u i d e l i n e s f o r the e v a l u a t i o n of g e n e r a l Data Base Systems. Chapter 3 p r e s e n t s an e v a l u a t i o n of the method of a n a l y s i s used i n t h i s s tudy and the g e n e r a l c o n c l u s i o n s drawn from the s t u d y . Appendix 1 c o n t a i n s d e t a i l e d answers t o most of the q u e s t i o n s proposed by the DBDG r e g a r d i n g the e v a l u a t i o n of the IMS/VS system. Appendix 2 c o n t a i n s the unanswered q u e s t i o n s . Appendix 3 c o n t a i n s a g l o s s a r y of terms used by the DBDG. i i i TABLE OF CONTENTS Chapter 1: IMS/VS Main F e a t u r e s 1 1.1 I n t r o d u c t i o n 1 1.2 Stor a g e O r g a n i z a t i o n 3 1.3 Database Design 5 Chapter 2: IMS/VS: An e v a l u a t i o n 13 2.1. A p p l i c a t i o n Programming F a c i l i t i e s 13 2.2. A r c h i t e c t u r e , Computing environment, Parameter . L i m i t s and M u l t i t h r e a d i n g •. 18 2.3. Backup / Recovery / R e s t a r t 23 2.4. Communication F a c i l i t i e s 26 2.5. Concurrency 27 2.6. Data A d m i n i s t r a t i o n and Data D i c t i o n a r y 28 2.7. Data independence and user views 31 2.8. Data Model 32 2.9 Data S t o r a g e . . 34 2.10. D i s t r i b u t e d Database F a c i l i t i e s 39 2.11. E f f i c i e n c y 39 2.12. Human I n t e r f a c e 42 2.13. L o c a l Support F a c i l i t i e s 43 2.14. P o r t a b i l i t y 44 2.15. R e l i a b i l i t y 45 2.16. S e c u r i t y 47 2.17. Software Q u a l i t y 49 2.18. U t i l i t i e s 49 i v 2 . 1 9 IMS/VS Uses and c o s t s 50 2.20 IMS/VS A c c o m p l i s h e d O b j e c t i v e s 51 Chapter 3: Method E v a l u a t i o n 54 3.1 E v a l u a t i o n C r i t e r i a 54 3.2 Some Recommendations 56 Appendix 1 : D e t a i l e d E v a l u a t i o n 58 Appendix 2: Unanswered E v a l u a t i o n C r i t e r i a 103 Appendix 3: G l o s s a r y of terms 105 R e f e r e n c e s 106 ACKNOWLEDGMENT I wish to express my thanks to Dr. Paul Gilmore for his helpful and patient assistance during the preparation of this thesis. I also wish to thank the Department of Computer Science, University of British Columbia, for providing financial assistance throughout the course of my studies. 1 CHAPTER 1: IMS/VS MAIN FEATURES T h i s c h a p t e r p r o v i d e s i n t r o d u c t o r y i n f o r m a t i o n on the main IMS/VS f a c i l i t i e s . These f e a t u r e s a r e used t o c r e a t e and m a n i p u l a t e Data Bases i n an IMS/VS environment. The c h a p t e r has been d i v i d e d i n t h r e e s e p a r a t e s e c t i o n s . The f i r s t s e c t i o n c o n t a i n s an ov e r v i e w of the system and a d e s c r i p t i o n of i t s main o b j e c t i v e s . S e c t i o n two i n t r o d u c e s the d i f f e r e n t s t o r a g e o r g a n i z a t i o n s and the O p e r a t i n g Systems a c c e s s methods. S e c t i o n t h r e e d e s c r i b e s the Database d e s i g n t e c h n i q u e a v a i l a b l e . Emphasis i s g i v e n t o the e x i s t i n g l o g i c a l r e l a t i o n s h i p s which can be d e f i n e d between h i e r a r c h i e s . 1 . 1 I n t r o d u c t i o n IMS/VS i s an IBM Database Management System. I t was i n t r o d u c e d i n the e a r l y 60's as DL/I. T h i s f i r s t system was c o n s i d e r e d a pseudo language d e s i g n e d t o e x t e n d the c a p a b i l i t i e s of the COBOL language. L a t e r s e v e r a l v e r s i o n s and r e l e a s e s were produced and DL/1 e v o l v e d i n t o IMS/360. The IMS/360 System e v e n t u a l l y became the c u r r e n t IMS/VS. The IMS/VS v e r s i o n has i n c o r p o r a t e d many of the o p t i o n a l f e a t u r e s o f f e r e d by e a r l i e r r e l e a s e s . In a d d i t i o n , many of t h e r o u t i n e s i n s i d e the system have been m o d i f i e d and a r e i n c o n s t a n t r e v i e w t o meet the chan g i n g needs of the u s e r s . T h i s e v o l u t i o n and the p r o c e s s of ad d i n g f u n c t i o n s has made of IMS/VS a v e r y mature p r o d u c t . The c u r r e n t IMS/VS shows many of the t e c h n i c a l advances made i n the Database f i e l d , and uses the h i e r a r c h i c a l model f o r the im p l e m e n t a t i o n of a l l p h y s i c a l Data Bases. The IMS/VS has been 2 s u c c e s s f u l i n u s i n g the h i e r a r c h i c a l model and has t h e r e f o r e p o p u l a r i z e d i t . The IMS/VS s o f t w a r e i s d e s i g n e d as an open ended system t h a t u s e r s t a i l o r t o s u i t t h e i r p a r t i c u l a r e n v i r o n m e n t s . The c u r r e n t v e r s i o n of IMS/VS runs i n s e v e r a l IBM/370 machines and c o m p a t i b l e models. I t uses many of the f a c i l i t i e s of t he o p e r a t i n g systems OS/VS1, 0S/VS2 and MVS, e s p e c i a l l y f o r t e l e c o m m u n i c a t i o n s and t e r m i n a l s u p p o r t . A d d i t i o n a l p r o d u c t s which can enhance the IMS/VS performance, a r e o f f e r e d by IBM and o t h e r s o f t w a r e companies. The IMS/VS l o g i c a l p a r e n t and l o g i c a l c h i l d i d e a s a r e a new f e a t u r e which makes p a r t i a l n e t w o r k i n g f a c i l i t i e s and many-to-many r e l a t i o n s , p o s s i b l e . IMS/VS i s d i v i d e d i n t o two major components: Database and Data Communication. The Database component (DB) i s a p r e r e q u i s i t e f o r the Data Communication p a r t and i s the c o r e of the system. The DB component c o n t a i n s a l l the r o u t i n e s and f a c i l i t i e s n e c e s s a r y f o r the c r e a t i o n and maintenance of Data Bases. T h i s component can run o n - i t s - o w n r e s t r i c t e d t o a b a t c h - o n l y environment. The Data Communications component p r o v i d e s o n l i n e s u p p o r t and a r e a s o n a b l e degree of c o n c u r r e n c y . T h i s component handles a l l message p r o c e s s i n g t r a n s a c t i o n s and c o n t r o l s the normal o p e r a t i o n of t e r m i n a l s . In a d d i t i o n i t i s a p r e r e q u i s i t e f o r the i n s t a l l a t i o n of o p t i o n a l f e a t u r e s l i k e the F a s t P a t h F e a t u r e and the M u l t i p l e C o u p l i n g System. The F a s t P a t h F e a t u r e p r o v i d e s f a s t e r - t h a n - n o r m a l a c c e s s t o s e l e c t e d d a t a . The M u l t i p l e C o u p l i n g System F e a t u r e p r o v i d e s a c c e s s t o Database D i s t r i b u t i o n 3 \ \ / f a c i l i t i e s . IBM i s c o n s t a n t l y u p d a t i n g the IMS/VS system. T h i s i s r e f l e c t e d i n the numerous a d d i t i o n s , new o p t i o n s and changes from one IMS/VS v e r s i o n t o a n o t h e r . The IMS/VS system has e v o l v e d under the f o l l o w i n g permanent b a s i c o b j e c t i v e s . 1) Independence of the a p p l i c a t i o n program from the u n d e r l y i n g formats and a c c e s s methods used f o r d a t a i n p u t and o u t p u t . Program c o m p a t i b i l i t y from v e r s i o n t o v e r s i o n . New v e r s i o n s t o be e a s i l y handled by o l d v e r s i o n u s e r s and t o which a p p l i c a t i o n programs can be r e a d i l y adapted. The i n t r o d u c t i o n of the a d d i t i o n a l p r o d u c t IMS A p p l i c a t i o n Development F a c i l i t y (IMSADF) s i m p l i f i e d program w r i t i n g . 2) P o s s i b l e , f a i l u r e c o n d i t i o n s such as system c r a s h , hardware f a i l u r e and s t o r a g e media f a i l u r e s s h o u l d not a f f e c t Database and message i n t e g r i t y . These c o n d i t i o n s can i n c l u d e system, hardware, and s t o r a g e media f a i l u r e s . So f a r , s o f t w a r e p r o d u c t s have been enhanced w i t h hardware d e v i c e s such as N o n - i n t e r r u p t i b l e power s u p p l y and Warning d e v i c e s . 3) An i n t e g r a t e d Database and Data Communication system s h o u l d a l l o w c o n c u r r e n c y a c c e s s t o a Database w h i l e m a i n t a i n i n g i t s i n t e g r i t y . The e a r l y v e r s i o n s of IMS/360 s u p p o r t e d c o n c u r r e n c y r e s t r i c t e d t o b a t c h a p p l i c a t i o n s . In response t o the demand f o r a more f l e x i b l e system which would a l l o w o n l i n e c o n c u r r e n t updates, the C o n t r o l Program was m o d i f i e d and s e v e r a l l o c k p r o t o c o l p o l i c i e s were implemented w i t h l i m i t e d s u c c e s s . The s e a r c h f o r an i d e a l c o n c u r r e n t environment ended w i t h the i n c o r p o r a t i o n of the Program I s o l a t i o n F e a t u r e (PIF) , as a b u i l t - i n p a r t of IMS/VS. The PIF a l l o w s the e x e c u t i o n of c o n c u r r e n t programs as i f they were r u n n i n g a l o n e . C o n c u r r e n t programs can a c c e s s and update the same Data Base, w i t h l o c k i n g mechanism p r e s e r v i n g the i n t e g r i t y of the Database. Deadlock s i t u a t i o n s a r e d e t e c t e d and s o l v e d by t e r m i n a t i n g one of the programs i n v o l v e d and r e l e a s i n g i t s r e s o u r c e s . 1.2 S t o r a g e O r g a n i z a t i o n The IMS/VS system p r o v i d e s s e v e r a l t y p e s of s t o r a g e o r g a n i z a t i o n a d d r e s s e d by a r e s p e c t i v e s e t of r o u t i n e s , w i t h i n the IMS/VS C o n t r o l Program. Each s e t of r o u t i n e s has the same 4 name as the type of s t o r a g e o r g a n i z a t i o n i t a d d r e s s e s . The b a s i c t y p e s of s t o r a g e o r g a n i z a t i o n a r e : HSAM f o r H i e r a r c h i c a l S e q u e n t i a l A c cess Method, HISAM f o r H i e r a r c h i c a l Indexed S e q u e n t i a l A c c e s s Method, HIDAM f o r H i e r a r c h i c a l Indexed D i r e c t Access Method and HDAM f o r H i e r a r c h i c a l D i r e c t Access Method. The Databases a r e named a f t e r the type of s t o r a g e o r g a n i z a t i o n they use. The s t o r a g e o r g a n i z a t i o n t y p e s a r e not O p e r a t i n g System (OS) a c c e s s methods, but they i n t e r f a c e w i t h t r u l y OS methods t o r e t r i e v e the s t o r e d d a t a . A more complete d e s c r i p t i o n of these s t o r a g e o r g a n i z a t i o n s i s g i v e n i n s e c t i o n 2.9. In a d d i t i o n t o the above mentioned s t o r a g e o r g a n i z a t i o n s , IMS/VS o f f e r s a l t e r n a t i v e s t o r a g e o r g a n i z a t i o n s which a r e used as m i g r a t i o n t o o l s between an IMS/VS and a non-IMS/VS environment. These o p t i o n a l s t o r a g e o r g a n i z a t i o n s a re known as Simple HSAM, Simple HI SAM, and G e n e r a l i z e d S e q u e n t i a l A c c e s s Method (GSAM). They make i t p o s s i b l e t o use non-IMS/VS a p p l i c a t i o n programs w i t h IMS/VS d a t a f i l e s . S i m i l a r l y , t h r o u g h these o p t i o n a l s t o r a g e o r g a n i z a t i o n s i t i s p o s s i b l e t o use IMS/VS a p p l i c a t i o n programs w i t h non-IMS/VS d a t a f i l e s . IMS/VS p r o v i d e s u t i l i t i e s f o r the c o n v e r s i o n ( r e o r g a n i z a t i o n ) of Data Bases which use the o p t i o n a l s t o r a g e o r g a n i z a t i o n i n t o one of the f o u r b a s i c s t o r a g e o r g a n i z a t i o n t y p e s . Each s t o r a g e o r g a n i z a t i o n type uses d i f f e r e n t O p e r a t i n g System a c c e s s methods. The most common methods a r e : OS/VS S e q u e n t i a l A c c e s s Method (SAM), Indexed S e q u e n t i a l Access Method (ISAM), S e v e r a l v e r s i o n s of OS/VS S e q u e n t i a l Access Method (VSAM) and an s p e c i a l IMS/VS method c a l l e d the O v e r f l o w 5 S e q u e n t i a l A c c e s s Method (OSAM). The d i f f e r e n t s t o r a g e o r g a n i z a t i o n s were d e s i g n e d as e x t e n s i o n s of an O p e r a t i n g System a c c e s s method a l r e a d y i n e x i s t e n c e . T h i s i s not o n l y t r u e of the s t o r a g e o r g a n i z a t i o n s but i t i s a c h a r a c t e r i s t i c t h a t a p p l i e s t o many components of IMS/VS. 1.3 Database Design T h i s s e c t i o n w i l l i n t r o d u c e the main f a c i l i t i e s p r o v i d e d by IMS/VS f o r the d e s i g n and i m p l e m e n t a t i o n of Databases. I t i n t r o d u c e s terms and n o t a t i o n s e x c l u s i v e l y of IMS/VS. The IMS/VS data sublanguage (or Data Management F a c i l i t y ) i s c a l l e d DL/1. DL/1 p r o v i d e s a f a c i l i t y t o adapt IMS/VS Databases t o the user a p p l i c a t i o n s r e q u i r e m e n t s . A p p l i c a t i o n programs which use DL/1 d e a l w i t h the so c a l l e d a p p l i c a t i o n d a t a s t r u c t u r e s . These data s t r u c t u r e s d e f i n e the way i n which an a p p l i c a t i o n program w i l l "see" the d a t a ; thus the DL/1 i n t e r f a c e w i l l never a c c e s s e s the p h y s i c a l d a t a s t r u c t u r e . The a p p l i c a t i o n d a ta s t r u c t u r e s used by DL/1 c o n s i s t of one or more h i e r a r c h i c a l d a t a s t r u c t u r e s . The a p p l i c a t i o n programs use one of the t h r e e host l a n g u a g e s : C o b o l , PL/1 or Assembler t o d e s c r i b e each of the a p p l i c a t i o n d a t a s t r u c t u r e s . O r d i n a r y s u b r o u t i n e c a l l s p r o v i d e a c c e s s t o the d a t a . The f o l l o w i n g i s an example of DL/1 i n t e r f a c e e f f e c t s on d a t a r e p r e s e n t a t i o n . The t r a d i t i o n a l r e c o r d l a y o u t t o r e p r e s e n t data about a -department, employee and p r o j e c t can be seen i n f i g u r e 1.1. 6 F i g u r e 1 . 1 Each of t h e s e s e c t i o n s (Dept, Employee, P r o j e c t ) may have more than one f i e l d . For example, the employee s e c t i o n c o u l d c o n s i s t of employee name, employee a d d r e s s , employee s a l a r y . A t r a d i t i o n a l a p p l i c a t i o n program w i l l r e t r i e v e the d a t a i n e x a c t l y the same way as i t appears i n secondary s t o r a g e . The same d a t a appears r e c o r d e d i n f i g u r e 1.2. T h i s t i m e , however, the r e c o r d has been l a i d out f o l l o w i n g a DL/1 a p p l i c a t i o n d a t a s t r u c t u r e . The Dept, Employee and P r o j e c t s e c t i o n s a r e s e p a r a t e segments of d a t a . In c o n t r a s t t o most o t h e r the name "segment" i n s t e a d ' pf " r e c o r d " or " s e c t i o n " appears i n IMS/VS t e r m i n o l o g y . .The s t r u c t u r e i n f i g u r e 1.2 i s c a l l e d a h i e r a r c h i c a l d a t a s t r u c t u r e . Each o c c u r r e n c e of t h i s s t r u c t u r e i s c a l l e d a P h y s i c a l Database Record. One or more P h y s i c a l Database Records c o n s t i t u t e a P h y s i c a l Data Base. A p p l i c a t i o n programs are s p e c i f i e d t o show o n l y the d a t a i n d i c a t e d by the Data Base A d m i n i s t r a t o r , t o the u s e r s . The d a t a t o be viewed by the u s e r s i s known by the name of L o g i c a l Databases. A L o g i c a l Database can be c o n s i d e r e d as a sub-h i e r a r c h y of a P h y s i c a l Data Base. I n a l l c a s e s the r o o t i s p a r t of the L o g i c a l Database. 7 Dept Data Base Dept Employee P r o j e c t F i g u r e 1.2 I t i s c l e a r , from f i g u r e 1.2, t h a t the h i e r a r c h i c a l d a t a model may p r e s e n t some problems. The one-to-many r e l a t i o n s impose s e v e r a l r e s t r i c t i o n s . I f , f o r example, an employee works f o r more than one department we w i l l need t o have more than one p h y s i c a l Database segment w i t h the same i n f o r m a t i o n about the employee. The same problem a r i s e s when new P h y s i c a l Data Bases (such as the one shown i n f i g u r e 1.3) are d e f i n e d . These new Data Bases need t o use one or more segments ("employee" i n the example of f i g u r e 1.3) a l r e a d y d e f i n e d i n o t h e r P h y s i c a l Data Bases. T h i s problem i s s o l v e d t h r o u g h the i n t r o d u c t i o n of a d d i t i o n a l p o i n t e r s between segments w i t h i n the same or d i f f e r e n t P h y s i c a l Data Bases. These p o i n t e r s p r o v i d e a l o g i c a l r e l a t i o n s h i p among segments from the same or d i f f e r e n t h i e r a r c h i e s . T h i s l o g i c a l r e l a t i o n s h i p be d e f i n e d o n l y w i t h HIDAM and/or HDAM P h y s i c a l Data Bases. Be i n g a b l e t o d e f i n e new h i e r a r c h i c a l s t r u c t u r e s a l l o w s the user t o a v o i d redundancy and d u p l i c a t i o n of i n f o r m a t i o n . 8 O f f i c e Database O f f i c e Phone Employee F i g u r e 1.3 An example of a l o g i c a l r e l a t i o n s h i p i s shown i n f i g u r e 1.4 which shows two P h y s i c a l Data Bases: The " O f f i c e - D B " and the "Dept-DB". In t h i s case t h e r e i s a u n i d i r e c t i o n a l l o g i c a l r e l a t i o n s h i p : the r e l a t i o n s h i p between the "Employee" and " O f f i c e " segments. L o g i c a l Database Off ice-DB Dept-DB O f f i c e Dept Phone Employee P r o j e c t F i g u r e 1.4 D e f i n i t i o n of a l o g i c a l r e l a t i o n s h i p i n v o l v e s the s p e c i f i c a t i o n of a l o g i c a l c h i l d ( i n t h i s example, the employee) and a l o g i c a l p a r e n t segment ( i n t h i s example, O f f i c e ) . The 9 y c h i l d segment w i l l have two a c c e s s p a t h s : one c a l l e d the p h y s i c a l a c c e s s p a t h which goes t h r o u g h the p h y s i c a l p a r e n t and another c a l l e d the l o g i c a l a c c e s s p a t h which goes t h r o u g h the l o g i c a l p a r e n t . Both a c c e s s p a t h s can c o n c u r r e n t l y be used by a program. IMS/VS a l s o a l l o w s f o r the d e f i n i t i o n of b i d i r e c t i o n a l l o g i c a l r e l a t i o n s h i p s between segments of one or more P h y s i c a l Data Bases. I f a b i d i r e c t i o n a l l o g i c a l r e l a t i o n s h i p i s d e f i n e d between the segments " o f f i c e " and "employee" o"f f i g u r e 1.4, h i e r a r c h i c a l s t r u c t u r e s such as the ones shown i n f i g u r e 1.5 and 1.6 can be o b t a i n e d . Dept Employee O f f i c e P r o j e c t Phone F i g u r e 1.5 The l o g i c a l r e l a t i o n s h i p p o i n t e r s a re l o c a t e d i n segment p r e f i x e s m a i n t a i n e d and c o n t r o l l e d by IMS/VS-DB s o f t w a r e . These p o i n t e r s a re s p e c i f i e d t h r o u g h parameter e n t r i e s made d u r i n g the 10 Data Base D e f i n i t i o n p r o c e s s . O f f i c e Phone ±_ , P r o j e c t F i g u r e 1.6 The d e f i n i t i o n of each P h y s i c a l Data Base i s made i n two l e v e l s . Both l e v e l s a r e c o n t r o l l e d by the Data Base A d m i n i s t r a t o r and a r e m a i n t a i n e d i n s e p a r a t e l i b r a r i e s . The f i r s t l e v e l of P h y s i c a l Data Base d e f i n i t i o n i s known as Database D e s c r i p t i o n (DBD).It c o n s i s t s of st a t e m e n t s d e s c r i b i n g the o v e r a l l P h y s i c a l Data Base h i e r a r c h i c a l s t r u c t u r e and each of i t s segments. These d e s c r i p t i o n s t a t e m e n t s a re made thr o u g h macro-assembler i n s t r u c t i o n s and used as i n p u t f o r the u t i l i t y program DBDGEN i n p r o d u c i n g an o b j e c t code as o u t p u t . T h i s code i s the a c t u a l Data D e s c r i p t i o n t h a t w i l l be used whenever a Data Base t r a n s a c t i o n t a k e s p l a c e . The o b j e c t code i s s t o r e d i n the DBD l i b r a r y . T h i s a c t u a l Data d e s c r i p t i o n w i l l a l l o w DL/1 t o use the p h y s i c a l d a t a s t o r a g e i n accordance w i t h 11 the r e q u i r e m e n t s of an a p p l i c a t i o n d a t a s t r u c t u r e . The P h y s i c a l Data Base segments can be l i n k e d t o g e n e r a t e l o g i c a l Databases t h r o u g h the same u t i l i t y program DBDGEN. The s p e c i f i c a t i o n of l o g i c a l c h i l d and l o g i c a l p a r e n t segments can be done t h r o u g h macro assembler i n s t r u c t i o n s . P r i o r t o t h e d e f i n i t i o n of a L o g i c a l Database the P h y s i c a l Data B a s e ( s ) have t o be d e f i n e d . IMS/VS p r o v i d e s f a c i l i t i e s f o r a c c e s s i n g d a t a u s i n g secondary i n d e x e s . The use of secondary indexes r e q u i r e s the g e n e r a t i o n of a l o g i c a l Data Base: One of the f i e l d s i n a l o g i c a l Database segment i s s p e c i f i e d as the s e c o n d a r y index or a l t e r n a t i v e key. Search o p e r a t i o n s use t h i s f i e l d as i f i t were the o n l y "key segment f i e l d " . The second l e v e l of Database d e f i n i t i o n i s the g e n e r a t i o n of Program S p e c i f i c a t i o n B l o c k s (PSB). Each PSB c o n s i s t s of one or more Program Communication B l o c k s (PCBs). Each PCB d e f i n e s a p a r t i a l (or t o t a l ) h i e r a r c h y of a P h y s i c a l or L o g i c a l Database. Every a p p l i c a t i o n program needs t o have a PSB b e f o r e i t can run. The Program S p e c i f i c a t i o n B l o c k s d e f i n e u s e r s ' views and c o n t a i n a l l a u t h o r i z a t i o n s t o a c c e s s a p a r t i c u l a r Data Base. A l l a c c e s s a u t h o r i z a t i o n s a re implemented i n s i d e a p a r t i c u l a r PCB. Segments and f i e l d s t o which u s e r s have a c c e s s a r e named " s e n s i t i v e " . Those segments and f i e l d s not named t h i s way w i l l be s k i p p e d d u r i n g the u s e r view. The PSBGEN f a c i l i t y g e n e r a t e s Program S p e c i f i c a t i o n B l o c k s through macro assembler i n s t r u c t i o n s . These i n s t r u c t i o n s s p e c i f y the Data Bases t o be used and the a u t h o r i z e d segments and f i e l d s 1 2 w i t h i n each Data Base. The output i s s t o r e d i n the PSB l i b r a r y and i s r e t r i e v e d when the a p p l i c a t i o n program i s s c h e d u l e d t o run . The Data Base D e s c r i p t i o n and the Program S p e c i f i c a t i o n B l o c k a re used t o g e n e r a t e the A p p l i c a t i o n C o n t r o l B l o c k (ACB) which i s s t o r e d i n the ACB l i b r a r y . B e f o r e a program i s sc h e d u l e d t o r u n , the ACB can e i t h e r be r e t r i e v e d from the ACB l i b r a r y and l o a d e d t o main memory or c o n s t r u c t e d from the DBD's and the PSB. The a c c e s s a u t h o r i z a t i o n s a r e f i r s t checked a g a i n s t t h e ACB and the PCB masks s p e c i f i e d i n the program. Changes i n the s p e c i f i c a t i o n s c o n t a i n e d i n the Data Base D e s c r i p t i o n may produce some i n c o n s i s t e n c i e s i n the user views a l r e a d y i n e x i s t e n c e , i . e , the d a t a segments used t o produce the user views a r e dependent on Data Base D e s c r i p t i o n changes. A l t h o u g h i t i s t r u e t h a t a d d i n g segments i n c e r t a i n p a r t s of the Data D e s c r i p t i o n w i l l not need c h a n g i n g PSB's or a p p l i c a t i o n programs, more severe changes may produce o t h e r e f f e c t s . For example, d e l e t i n g a segment or r e s t r u c t u r i n g i t , may r e q u i r e the r e - g e n e r a t i o n of some PSB's and/or the r e c o m p i l a t i o n of some a p p l i c a t i o n programs. In a d d i t i o n the d e l e t i o n of a segment by an a u t h o r i z e d a p p l i c a t i o n program w i l l r e s u l t i n the d e l e t i o n of a l l the c h i l d r e n segments r e g a r d l e s s of whether they were d e c l a r e d s e n s i t i v e or not i n t h e i r r e s p e c t i v e PSB. 13 CHAPTER 2: IMS/VS: AN EVALUATION T h i s c h a p t e r p r o p o s e s t o i d e n t i f y the s t r o n g e s t and weakest f e a t u r e s of the IMS/VS system. The IMS/VS f u n c t i o n s and/or c h a r a c t e r i s t i c s a r e here e v a l u a t e d i n accordance w i t h what was suggested by the Data Base D i s c u s s i o n Group (DBDG) of UBC. The DBDG's q u e s t i o n s and t h e i r s p e c i f i c answers a r e p r e s e n t e d i n Appendix 1. 2.1. A p p l i c a t i o n Programming F a c i l i t i e s The d a t a m a n i p u l a t i o n language used w i t h IMS/VS i s c a l l e d Data Language One (DL/1). DL/l p r o v i d e s the i n t e r f a c e between a user program and IMS/VS. I t can be in v o k e d from one of the t h r e e host languages: C o b o l , PL/1, or Assembler by means of o r d i n a r y s u b r o u t i n e c a l l s . There a r e v e r y few d i f f e r e n c e s between an IMS/VS and a non-IMS/VS environment and they imply an e x t r a overhead. When t h e r e are d i f f e r e n c e s they a re r e f l e c t e d i n the Input/Output o p e r a t i o n s . The Input/Output o p e r a t i o n s a re more s o p h i s t i c a t e d i n an IMS/VS system, s i n c e the d a t a i s t r a n s f e r r e d i n segment form. These d a t a segments a r e p a r t of r e c o r d s w i t h i n h i e r a r c h i c a l s t r u c t u r e s . The d i f f e r e n c e s between an IMS/VS and a non-IMS/VS environment a r e almost t r a n s p a r e n t t o the user s i n c e the IMS/VS system h a n d l e s the a d d i t i o n a l overhead through i t s a c c e s s methods. The programmer need not be concerned w i t h the mentioned d i f f e r e n c e s . The b a s i c I/O o p e r a t i o n s codes of IMS/VS a r e GET ( s i x v a r i a t i o n s ) , REPLACE, INSERT and DELETE. T h e i r uses a r e 1 4 d e s c r i b e d below: O p e r a t i o n F u n c t i o n Code GU GET UNIQUE: P r o v i d e s d i r e c t a c c e s s t o a Database or t e r m i n a l f o r the r e t r i e v a l of a s p e c i f i c segment from. GN GET NEXT: P r o v i d e s s e q u e n t i a l a c c e s s GET t o a Database or t e r m i n a l f o r the r e t r i e v a l of an s p e c i f i c segment. GNP GET NEXT WITHIN PARENT: Another s e q u e n t i a l a c c e s s t o a Database or t e r m i n a l . I t s range i s l i m i t e d t o a s p e c i f i c p a r e n t . GHU, GHN, GHNP: Co r r e s p o n d i n g t o the GU, GN and GNP o p e r a t i o n s w i t h the H s i g n i f y i n g HOLD. They o p e r a t i o n s a r e used w i t h the REPLACE and/or DELETE o p e r a t i o n s t o p r o v i d e a l o c k . ISTR INSERT: T h i s i s a PUT o p e r a t i o n used f o r i n i t i a l l o a d i n g or f o r a d d i n g d a t a t o a Database. REPL, DLET REPLACE and DELETE: These two o p e r a t i o n s work i n c o n j u n c t i o n w i t h the t h r e e GET HOLD o p e r a t i o n s . A f t e r r e t r i e v a l , segments can be w r i t t e n back (REPL) or d e l e t e d (DLET). The REPL o p e r a t i o n f a c i l i t a t e s u p d a t i n g w h i l e DLET a c c o m p l i s h e s p u r g i n g . A s i n g l e program can invoke s e v e r a l views of a s i n g l e Database, or i t can r e f e r t o s e v e r a l Databases. The Databases s t r u c t u r e s needed by a program a r e c o n t a i n e d i n i t s Program S p e c i f i c a t i o n B l o c k (PSB). A PSB c o n s i s t s of one or more Program Communication B l o c k s (PCB). A PCB i s r e q u i r e d f o r each view of a Database t h a t a program i n t e n d s t o use. The Data Base A d m i n i s t r a t o r p r e p a r e s and m a i n t a i n s a l l e x i s t i n g PSBs. A program i s r e s t r i c t e d t o the a c c e s s a u t h o r i z a t i o n s c o n t a i n e d i n i t s PSB. For o n l i n e A p p l i c a t i o n programs the PSB and the Data Base D e s c r i p t i o n (DBD) are used t o g e n e r a t e an A p p l i c a t i o n 15 C o n t r o l B l o c k (ACB). The ACB i s l o a d e d i n t o the main memory b e f o r e the a p p l i c a t i o n program t a k e s c o n t r o l . DL/1 i s a v e r y easy and p o w e r f u l Data M a n i p u l a t i o n Language. A DL/1 c a l l may d e a l w i t h one or more segments i n the h i e r a r c h i c a l p a t h , and one or more Segment Search Arguments (SSA). A SSA i s a segment name t h a t may be f o l l o w e d by one or more command codes and one or more q u a l i f i c a t i o n s t a t e m e n t s . The q u a l i f i c a t i o n s t a t ements c o n s i s t of a s e t of comparison e x p r e s s i o n s connected by the boolean o p e r a t o r s 'AND' or 'OR'. The command codes modify the way i n which a s e a r c h w i l l be performed. As a r e s u l t of the s e c o n t r o l o p t i o n s a DL/1 c a l l may get . v e r y c o m p l i c a t e d , and when e x e c u t e d i t may produce unexpected r e s u l t s . For t h i s reason DL/1 i s c o n s i d e r t o be a poor language f o r s t r u c t u r a l m a n i p u l a t i o n . User views a r e known as L o g i c a l Databases, and they r e p r e s e n t a h i e r a r c h i c a l and s t r u c t u r a l r e l a t i o n s h i p between da t a segments. The o v e r a l l q u a l i t y of user d i a g n o s t i c s i s good. F a c i l i t i e s f o r e n c r i p t i o n / d e c r i p t i o n a r e a v a i l a b l e t h r o u g h user w r i t t e n r o u t i n e s and the segment e d i t / c o m p r e s s i o n e x i t f a c i l i t i e s . There i s no b u i l t - i n r e p o r t g e n e r a t o r and t h e r e a r e no s o r t i n g f a c i l i t i e s i n s i d e the system. As w i t h many p a r t s of the system, the a p p l i c a t i o n environment i s i n c o n s t a n t r e v i s i o n and improvement. New f a c i l i t i e s a r e always o f f e r e d as s e p a r a t e p r o d u c t s . The more i m p o r t a n t s p r o d u c t s a re the IMS A p p l i c a t i o n Development F a c i l i t y (IMSADF), the I n t e r a c t i v e Query F a c i l i t y (IQF) and the F a s t P a t h F e a t u r e ( F P F ) . 16 IMSADF i s o f f e r e d as a t o o l f o r a more e f f i c i e n t development of a p p l i c a t i o n programs. I n c l u d e d a r e program modules t h a t are a b l e t o d i r e c t l y e xecute DL/1 c a l l s , e d i t i n p u t d a t a , format d i s p l a y s f o r c e r t a i n IBM d e v i c e s , p r o v i d e a c e r t a i n degree of s e c u r i t y , and r o u t e messages between a p p l i c a t i o n programs and system u s e r s . One of the p r i m a r y o b j e c t i v e s of IMSADF i s the r e d u c t i o n t o a minimum of programming needs. The package i s composed of a c e r t a i n number of f u n c t i o n a l program modules. These modules are a b l e t o pe r f o r m the b a s i c t a s k s found i n many of the most common programming a p p l i c a t i o n s . Other r o u t i n e s c o n t a i n the l o g i c r e q u i r e d t o combine e x i s t i n g f u n c t i o n a l program modules i n t o e x e c u t a b l e IMS/VS a p p l i c a t i o n programs. For a p p l i c a t i o n s whose r e q u i r e m e n t s exceed the c u r r e n t c a p a b i l i t i e s of IMSADF, e x i t s a re p r o v i d e d so t h a t the user can a t t a c h modules and s u b r o u t i n e s of h i s own t o enhance or t o add f u n c t i o n s not c o n t a i n e d w i t h i n the f a c i l i t y . IQF i s a query language f o r o n l i n e d a t a r e t r i e v a l . I t s s t r u c t u r e i s v e r y s i m p l e and c o n s i s t s of commands. P r e d e f i n e d s c r e e n s a r e p r o v i d e d f o r easy d i s p l a y of d a t a . S o r t i n g f a c i l i t i e s a r e b u i l t - i n and a r e in v o k e d w i t h the s o r t command. IQF does not p r o v i d e any type of update c a p a b i l i t i e s . The F a s t Path F e a t u r e (FPF) i s a p r o d u c t which p r o v i d e s r a p i d a c c e s s t o c e r t a i n Databases. Because Databases u s i n g the F a s t P a t h F e a t u r e r e q u i r e s p e c i a l d ata o r g a n i z a t i o n , i t i s m a i n l y used w i t h h e a v i l y used d a t a . In the E f f i c i e n c y s e c t i o n t h e r e i s a more complete d e s c r i p t i o n of FPF. 17 S t r e n g t h s 1) A p p l i c a t i o n programs can invoke s e v e r a l views of a s i n g l e database or of s e v e r a l d a t a b a s e s . 2) DL/1 i s a v e r y easy and p o w e r f u l d a t a m a n i p u l a t i o n language, e s p e c i a l l y f o r s e a r c h o p e r a t i o n s . 3) There i s a good support f o r common data p r o c e s s i n g environments t h r o u g h the host languages PL/1 and COBOL. Weaknesses 1) DL/I i s not a modern language f o r s t r u c t u r a l m a n i p u l a t i o n . 2) The se m a n t i c s of DL/1 i s not w e l l d e f i n e d . C o n t r o l o p t i o n s sometimes can produce unexpected r e s u l t s . 3) Every a p p l i c a t i o n program must be e x p l i c i t l y c o n f i g u r e d t o IMS/VS by a g e n e r a t i o n p r o c e s s done by the DBA. T h i s i s i n c o n v e n i e n t l y s t a t i c . 4) The system has so many and d i f f e r e n t o p t i o n s i n the a r e a s of a p p l i c a t i o n c o n f i g u r a t i o n and da t a d e f i n i t i o n t h a t i t can be d i f f i c u l t t o use. 5) O n l i n e a p p l i c a t i o n programs can not d i r e c t l y r e f e r e n c e non IMS/VS d a t a s e t s . 6) There i s no comprehensive v e n d o r - s u p p l i e d r e p o r t g e n e r a t o r . 7) There i s too much d i f f e r e n c e between o n l i n e and b a t c h a p p l i c a t i o n p r o c e s s i n g . B a t c h a p p l i c a t i o n and o n l i n e a p p l i c a t i o n programs run a c c o r d i n g t o d i f f e r e n t r u l e s . 18 2.2. A r c h i t e c t u r e , Computing environment, Parameter L i m i t s and M u l t i t h r e a d i n g As mentioned i n Chapter 1, t h e r e i s no c l e a r d i s t i n c t i o n between the O p e r a t i n g System (OS) and the IMS/VS f u n c t i o n s . Many Database o p e r a t i o n s or f e a t u r e s use the f a c i l i t i e s a l r e a d y p r o v i d e d by the OS or are an e x t e n s i o n of the s e f a c i l i t i e s . IMS/VS has been d e s i g n e d as an e x t e n s i o n of the O p e r a t i n g System, and i t runs as an a u t h o r i z e d program w i t h h i g h p r i o r i t y . The d e s i g n e r s , i n s t e a d of c i r c u n v e n t i n g the OS f a c i l i t i e s , have t r i e d t o ex t e n d them. The two major d i v i s i o n w i t h i n IMS/VS a r e : the Database (DB) p a r t and the Data Communications (DC) p a r t . The DB i s a p r e r e q u i s i t e f o r the DC and can be run on a s t a n d a l o n e b a s i s l i m i t i n g the system t o a b a t c h - o n l y environment. The DB i s the c o r e of the system and p r o v i d e s s u pport f o r the d e s c r i p t i o n , c r e a t i o n , maintenance, r e o r g a n i z a t i o n , a c c e s s , r e c o n s t r u c t i o n and s h a r i n g of a l l Databases i n the system. The DC handles a l l s e r v i c e s r e l a t e d t o t e r m i n a l management and i n p u t / o u t p u t messages and p r o v i d e s the n e c e s s a r y i n t e r f a c e w i t h the OS t o support messages p a s s i n g between t e r m i n a l s and the system. The s e p a r a t i o n between the DB and the DC i s not t o t a l l y d e f i n e d . Some f u n c t i o n s have been implemented i n both p l a c e s a t the same t i m e , and i t i s not always c l e a r t o which major d i v i s i o n they b e l o n g . IMS/VS uses e x t e n s i v e l y the concept of O p e r a t i n g System R e g i o n . The IMS/VS C o n t r o l Program, which r e s i d e s i n the IMS/VS 19 C o n t r o l R e g i o n , o v e r s e e s and manages most of the major o n l i n e a c t i v i t i e s . Among those f a c i l i t i e s a r e the DL/1 i n t e r f a c e , t e l e c o m m u n i c a t i o n s , and the c o n t r o l of a l l a c c e s s t o o n l i n e Databases. In a d d i t i o n t o the C o n t r o l R e g i o n , a t y p i c a l o n l i n e IMS/VS i n s t a l l a t i o n w i l l c o n s i s t s of a m i x t u r e of o n l i n e p r o c e s s i n g r e g i o n s known as Message P r o c e s s i n g Regions (MPR) and B a t c h Message P r o c e s s i n g Regions (BMPR). The MPR a r e the OS Regions where o n l i n e a p p l i c a t i o n programs are e x e c u t e d . The BMPR p r o v i d e s f a c i l i t i e s f o r the o n l i n e e x e c u t i o n of B a t c h programs. The IMS/VS Batc h environment i s s t r u c t u r e d as a s e p a r a t e OS r e g i o n known as Batc h R e g i o n . T h i s r e g i o n e x e c u t e s i n d e p e n d e n t l y from the C o n t r o l R e g i o n . The e x e c u t i o n of a B a t c h Region i s c o n s i d e r e d t o be a s e p a r a t e OS j o b r u n n i n g c o n c u r r e n t l y w i t h the IMS/VS C o n t r o l R e g i o n . Batch Regions are r e s t r i c t e d t o non-o n l i n e B a t c h programs. F i g u r e 2.1 shows a p i c t o r i a l r e p r e s e n t a t i o n of the s e a r c h i t e c t u r a l f a c t s . The use of s e p a r a t e r e g i o n s i n IMS/VS p r o v i d e s f o r some of i t s a r c h i t e c t u r a l s t r e n g t h s . The o n l i n e C o n t r o l Program i s i s o l a t e d and t h i s p r o v i d e s a n a t u r a l p r o t e c t i o n a g a i n s t u n a u t h o r i z e d use. In the same way, as u s e r s programs run i n s e p a r a t e r e g i o n s they a r e p r o t e c t e d from each o t h e r . The system does not n e c e s s a r i l y become u n a v a i l a b l e because of u s e r ' s e r r o r s . I n f a c t , an a p p l i c a t i o n program can, a t most, a b n o r m a l l y end the r e g i o n where i t i s o p e r a t i n g . 2 0 IMS IMS MESSAGE IMS BATCH MSG CONTROL PROCESSING PROCESSING REGION REGION REGION O n l i n e O n l i n e Program B a t c h BATCH REGION Pure Ba t c h IMS/VS makes e x t e n s i v e use of OS/VS l o a d l i b r a r i e s . The most i m p o r t a n t a r e the DBD l i b r a r y , c o n t a i n i n g a l l complete Database d e s c r i p t i o n s ; the PSB l i b r a r y , c o n t a i n i n g the c o m p i l e d Program S p e c i f i c a t i o n B l o c k s ( P S B ' s ) ; and the ACB l i b r a r y c o n t a i n i n g the A p p l i c a t i o n C o n t r o l B l o c k s . B e f o r e an a p p l i c a t i o n program i s s c h e d u l e d f o r e x e c u t i o n , IMS/VS must have a v a i l a b l e the DBDs and the PSB c o n t r o l b l o c k s . These c o n t r o l b l o c k s a r e merged and expanded i n t o an IMS/VS i n t e r n a l format c a l l e d " A p p l i c a t i o n C o n t r o l B l o c k s " (ACB) which can be saved i n the ACB l i b r a r y . A f a c i l i t y c a l l e d the A p p l i c a t i o n C o n t r o l B l o c k Maintenance can be used f o r p r e - b u i l d i n g , i n an o f f l i n e mode, the ACBs and f o r s t o r i n g them i n t o the ACB l i b r a r y . The p r e -b u i l d i n g of ACB i s r e q u i r e d f o r a DB/DC system, w h i l e f o r a DB i t i s o p t i o n a l . B e f o r e c o n t r o l i s passed t o a program, IMS/VS g e t s the ACB from the ACB l i b r a r y , or i t c o n s t r u c t s i t from the 21 PSB and the DBD. The maintenance of t h e s e l i b r a r i e s i s the r e s p o n s i b i l i t y of the Data Base A d m i n i s t r a t o r . IMS/VS o f f e r s d i f f e r e n t o p t i o n s f o r implementing d a t a s t o r a g e . The most i m p o r t a n t a r e : HSAM, HISAM, HIDAM and HDAM. HSAM and HISAM a r e used when s e q u e n t i a l p r o c e s s i n g w i l l be the main a c t i v i t y , w h i l e HIDAM and HDAM are used when the r e f e r e n c e i s a t random and d i r e c t a c c e s s t o segments i s r e q u i r e d . HSAM o f f e r s h i g h s t o r a g e e f f i c i e n c y w i t h poor f u n c t i o n a l i t y ( no d e l e t i o n s , no updates, and i n s e r t i o n s may be made o n l y w i t h i n i t i a l l o a d i n g ) . Both h i e r a r c h i c a l methods HIDAM and HDAM o f f e r g r e a t f l e x i b i l i t y due t o d i r e c t a c c e s s t o r o o t segments, but the d a t a tends t o be fragmented. See Data S t o r a g e s e c t i o n for.more d e t a i I s . A c e r t a i n degree of a u t o m a t i c r e o r g a n i z a t i o n i s o f f e r e d f o r d a t a b a s e s of t h e h i e r a r c h i c a l d i r e c t type (HIDAM and/or HDAM). IMS/VS a l l o c a t e s and r e c l a i m s s t o r a g e space as segments a r e i n s e r t e d and/or d e l e t e d . When the DC f e a t u r e i s i n s t a l l e d , a Master T e r m i n a l O p e r a t o r (MTO) i s r e q u i r e d t o monitor the a c t i v i t y of the system, make o n l i n e o p e r a t i o n a l a d j u s t m e n t s , and r e a c t t o any u n u s u a l c o n d i t i o n s i n the system. The MTO a c t s as a system r e s o u r c e c o n t r o l l e r f o r communication, s c h e d u l i n g and maintenance of the system. For most of h i s f u n c t i o n s the MTO uses the Master T e r m i n a l (MT). The MT p r o v i d e s f a c i l i t i e s s i m i l a r t o the c o n s o l e f o r the OS. There i s one MT per IMS/VS i n s t a l l a t i o n ; however i n case of f a i l u r e the system c o n s o l e can be used as MT. 22 In a d d i t i o n t o the u s u a l p h y s i c a l t e r m i n a l s the DC p a r t s u p p o r t s l o g i c a l t e r m i n a l s . A l o g i c a l t e r m i n a l i s a name which i s r e l a t e d t o a p h y s i c a l t e r m i n a l . More than one l o g i c a l t e r m i n a l can be a s s i g n e d t o an s p e c i f i c p h y s i c a l t e r m i n a l , and the MTO can r e a s s i g n l o g i c a l t e r m i n a l s t o o t h e r p h y s i c a l t e r m i n a l s . Parameter l i m i t s f o r most f a c i l i t i e s of IMS/VS have a good range. A Database can occupy as much s t o r a g e as i t needs. A maximum of 5000 Databases a r e a l l o w e d and the number of p h y s i c a l and l o g i c a l t e r m i n a l s s h o u l d not be more than 5000. There i s a maximum of 15 segment t y p e s i n any h i e r a r c h i c a l d i r e c t i o n a l p a t h , a maximum of 255 d i f f e r e n t segment t y p e s per h i e r a r c h i c a l s t r u c t u r e , and no more than 255 f i e l d s per segment. S t r e n g t h s 1) The o n l i n e c o n t r o l r e g i o n i s o l a t e s the DBMS c o n t r o l program, a l l o w i n g a n a t u r a l p r o t e c t i o n from the u s e r s . 2) The use of s e p a r a t e r e g i o n s f o r s e p a r a t e a p p l i c a t i o n s g i v e s good i s o l a t i o n between programs and the system. 3) The h o s t - l a n g u a g e i n t e r f a c e (the DL/1 i n t e r f a c e ) i s w e l l l o c a l i z e d . Weaknesses 1) There i s no dynamic c o n f i g u r a t i o n d e f i n i t i o n of Databases, user views or a p p l i c a t i o n programs. 2) The o p e r a t i n g system i n t e r f a c e i s complex. I t i s d i f f i c u l t t o d i s t i n g u i s h between the IMS/VS system and the OS 23 f u n c t i o n s . 3) The s e p a r a t i o n between DB and DC i s not w e l l d e f i n e d . Some f a c i l i t i e s a re p a r t of the DB and of the DC a t the same ti m e . 2.3. Backup / Recovery / R e s t a r t Most of the Backup/ R e c o v e r y / R e s t a r t o p e r a t i o n s a r e a c c o m p l i s h e d w i t h the Data Base R e o r g a n i z a t i o n and Recovery u t i l i t i e s . As most of the u t i l i t i e s can be d e v e l o p e d semi-i n d e p e n d e n t l y from the r e s t of the system, new u t i l i t i e s and r e v i s i o n s a r e always i n c l u d e d i n new r e l e a s e s and v e r s i o n s . At the same time new hardware d e v i c e s , l i k e n o n - i n t e r r u p t i b l e power d e v i c e s , a r e o f f e r e d as enhancements t o the s o f t w a r e . The f l e x i b i l i t y , o v e r a l l ease of use and the wide v a r i e t y of s i t u a t i o n s t h e s e u t i l i t i e s c over make the Backup / Recovery / R e s t a r t one of the s t r o n g e s t p o i n t s of IMS/VS. The main f u n c t i o n of the Recovery u t i l i t i e s i s the r e s t o r a t i o n of d a t a s e t s t h a t have been p h y s i c a l damaged and the p r o d u c t i o n of backup c o p i e s . To such e f f e c t , IMS/VS p r o v i d e s a system l o g , which i s used i n a l l the r e c o v e r y f u n c t i o n s . The Data Base r e c o v e r y u t i l i t i e s u s u a l l y c o n s i s t of c o p y i n g the p h y s i c a l Database from time t o t i m e . The system l o g m a i n t a i n s a l l changes made t o the Database i n the i n t e r v e n i n g time between c o p y i n g . In the event t h a t the Database becomes damaged, i t can be r e s t o r e d by r e s t o r i n g the Database from the copy and then a p p l y i n g a l l l o g g e d changes ( s i n c e t h a t copy was made) t o the r e s t o r e d Database. 24 The system l o g i s an output of the IMS/VS C o n t r o l Program or the Batc h Region e x e c u t i o n . T h i s output can be used f o r d i f f e r e n t a s p e c t s l i k e s t a t i s t i c s , a c c o u n t i n g , and a l l r e c o v e r y and r e s t a r t o p e r a t i o n s of the system. W i t h i n the C o n t r o l Program t h e r e i s a r o u t i n e known as the system r e c o r d e r . T h i s r o u t i n e i s used f o r s t o r i n g most of the d a t a . IMS/VS p r o v i d e s s e v e r a l u t i l i t i e s t h a t can be used when the system l o g has t o be r e c o v e r e d or i s not complete, or when l o g d a t a i s l o s t as a r e s u l t of system f a i l u r e . Other u t i l i t i e s a r e p r o v i d e d t o a n a l y s e and produce the s t a t i s t i c a l r e p o r t s . The R e o r g a n i z a t i o n u t i l i t i e s d e a l p r i m a r i l y w i t h the i n i t i a l l o a d i n g of the d a t a and w i t h p h y s i c a l and l o g i c a l r e o r g a n i z a t i o n of e x i s t i n g Databases. These u t i l i t i e s a l l o w the i n s e r t i o n s of new segments i n c e r t a i n p a r t s of the h i e r a r c h y , m o d i f i c a t i o n of e x i s t i n g segments, and change of a c c e s s methods. There a r e f a c i l i t i e s f o r p a r t i a l r e o r g a n i z a t i o n of Databases. The many u t i l i t i e s a v a i l a b l e can c r e a t e some c o n f u s i o n about t h e i r use. On some o c c a s i o n s the use of one u t i l i t y i s not enough. The output of a u t i l i t y can be used as i n p u t t o o t h e r ( s ) u t i l i t i e s t o get the d e s i r e d e f f e c t s . A u t o m a t i c s t o r a g e r e o r g a n i z a t i o n i s o f f e r e d f o r HIDAM and HDAM Databases a t the c o s t of p o s s i b l e d a t a f r a g m e n t a t i o n and the i n t r o d u c t i o n of a d d i t i o n a l p o i n t e r s . The U t i l i t y C o n t r o l F a c i l i t y (UCF), a s e p a r a t e p r o d u c t , i s o f f e r e d as a s o l u t i o n t o some of the problems s p e c i f i e d i n the l a s t p a r a g r a p h . UCF p r o v i d e s p r o c e d u r e s f o r the semi-au t o m a t i c c o m b i n a t i o n and e x e c u t i o n of m u l t i p l e u t i l i t i e s i n c l u d e d i n the 25 system. The use of UCF presuppones a p r e v i o u s knowledge of the i n v o l v e d u t i l i t i e s . In g e n e r a l , a l l u t i l i t i e s i n IMS/VS run as s t a n d a r d OS/VS j o b s and can be i n i t i a t e d and c o n t r o l l e d from the Master T e r m i n a l . The Master T e r m i n a l p r o v i d e s c a p a b i l i t i e s f o r c o n t i n u o u s m o n i t o r i n g of the system and f o r d e t e c t i n g damaged d a t a b a s e s . The Master T e r m i n a l can d y n a m i c a l l y i n i t i a t e backup and r e c o v e r y f u n c t i o n s . R e s t a r t i n g of the system depends on the c o n d i t i o n s of the l a s t t e r m i n a t i o n . The c o n s o l e i n i t i a t e s the MT which i n t u r n i n i t i a t e s a l l major IMS/VS o p e r a t i o n s . R o l l b a c k and s y n c h r o n i z a t i o n p o i n t s a r e p r o v i d e d f o r easy r e c o v e r y and can be i n v o k e d s e m i a u t o m a t i c a l l y . A p p l i c a t i o n programs can re q u e s t r o l l b a c k and/or s y n c h r o n i z a t i o n p o i n t s e a s i l y and f a i r l y f r e e l y . S t r e n g t h s 1) Great f l e x i b i l i t y i n the use of r o l l b a c k and s y n c h r o n i z a t i o n p o i n t s . These can be s p e c i f i e d a t almost any p o i n t i n s i d e an a p p l i c a t i o n program. 2) Backup / Recovery / R e s t a r t f e a t u r e s a r e comprehensive, a l l o w i n g r e c o v e r y from almost e v e r y problem. 26 Weaknesses 1) Backup / Recovery / R e s t a r t r e q u i r e m e n t s c o n s t r a i n the a p p l i c a t i o n programming environment i n some awkward ways. 2) There are no a u t o m a t i c r e c o v e r y f u n c t i o n s . 2.4. Communication F a c i l i t i e s IMS/VS DB i s a b a t c h environment u s i n g s t a n d a r d O p e r a t i n g Systems communication f a c i l i t i e s . These f a c i l i t i e s a r e used t o p r o v i d e d communication between the Databases and the a p p l i c a t i o n program and f o r the g e n e r a t i o n of a l l messages. For IMS/VS DB/DC the DC p a r t of the system p r o v i d e s f o r most communication f a c i l i t i e s . These f a c i l i t i e s a r e implemented as e x t e n s i o n t o the e x i s t i n g O p e r a t i n g Systems f e a t u r e s , and i t i s d i f f i c u l t t o i s o l a t e them. The O p e r a t i n g System p r o v i d e s two communications f a c i l i t i e s : the B a s i c T elecommunication Access Method (BTAM) or the V i r t u a l T e l e c o m m u n i ca tion Access Method (VTAM). However, the use of one e x c l u d e s the o t h e r . I f VTAM i s used the i n s t a l l a t i o n can use the System Network F a c i l i t i e s (SNA) t o p r o v i d e w i t h more advanced t e l e c o m m u n i c a t i o n type f u n c t i o n s . The M u l t i p l e Systems C o u p l i n g (MSC), another o p t i o n a l p r o d u c t , p r o v i d e s f o r D i s t r i b u t e d Database F a c i l i t i e s and f o r the s h a r i n g of Databases between two or more IMS/VS i n s t a l l a t i o n s . 27 2.5. Concurrency The Program I s o l a t i o n F e a t u r e (PIF) p r o v i d e s most of the support f o r the e x e c u t i o n of c o n c u r r e n t a p p l i c a t i o n programs. T h i s f e a t u r e i s o l a t e s the a c t i v i t y of an a p p l i c a t i o n program from o t h e r c o n c u r r e n t a p p l i c a t i o n p r o g r a m ( s ) , which can be working w i t h the same Database. In t h i s way segments compromised, because of update o p e r a t i o n s a r e not a v a i l a b l e t o o t h e r programs. When a segment i s l o c k e d , the program i n d i c a t e s , by r e a c h i n g a s y n c h r o n i z a t i o n p o i n t , t h a t the d a t a i t has m o d i f i e d or c r e a t e d i s c o n s i s t e n t , , complete and a v a i l a b l e t o o t h e r programs. A s y n c h r o n i z a t i o n p o i n t i s reached when the next DL/1 c a l l i s e x e c u t e d or when a program t e r m i n a t e s . In a d d i t i o n , s y n c h r o n i z a t i o n p o i n t s can be r e q u e s t e d a t s e v e r a l p o i n t s i n a program. The PIF uses enqueue/dequeue r o u t i n e s t o enqueue a f f e c t e d database elements r e q u i r e d by more than one a p p l i c a t i o n program. These r o u t i n e s a r e a b l e t o d e t e c t d e adlock s i t u a t i o n s . In the case of a d e a d l o c k , one of the programs i n v o l v e d i s t e r m i n a t e d w i t h a s p e c i a l s t a t u s code and i t s r e s o u r c e s a r e r e l e a s e d . G r a n u l a r i t y of l o c k s i s down t o segment l e v e l , p r o v i d i n g a r e a s o n a b l e amount of c o n c u r r e n c y . Locks can be e x c l u s i v e or s h a r e d , and can be s e t a t any t i m e . E x c l u s i v e l o c k s remain i n e f f e c t u n t i l the next s y n c h r o n i z a t i o n p o i n t . Shared l o c k s remain i n e f f e c t u n t i l the l o c k e d segment ceases t o be c u r r e n t . Segments may o n l y be updated when they are e x c l u s i v e l y l o c k e d . T r a n s a c t i o n s a r e s u p p o r t e d and, because they can be w r i t t e n u s i n g one of the host languages, a good amount of c o m p l e x i t y i s 28 a l l o w e d . The c o n c u r r e n t environment i s s l i g h t l y r e s t r i c t e d t o the Databases a t t a c h e d t o e i t h e r the C o n t r o l Region or the B a t c h Region. Programs r u n n i n g i n a r e g i o n dependent on the C o n t r o l Region cannot a c c e s s Databases a t t a c h e d t o the Bat c h Region and v i c e v e r s a . S t r e n g t h s 1) The l o c k support g u a r a n t e e s c o n s i s t e n c y of the d a t a m a i n t a i n e d i n a c o n c u r r e n t environment. 2) There i s good support f o r t r a n s a c t i o n s . T r a n s a c t i o n s can be w r i t t e n u s i n g the hos t language a l l o w i n g a g r e a t d e a l of c o m p l e x i t y . Weaknesses 1) The l o c k p r o t o c o l i s not deadlock f r e e . F u r t h e r m o r e , i n s t a l l a t i o n s have t o w r i t e t h e i r own r o u t i n e s t o handle t h o s e e x c e p t i o n s . 2) Databases a t t a c h e d t o the b a t c h environment cannot be a c c e s s e d c o n c u r r e n t l y from the o n l i n e environment and v i c e v e r s a . 2.6. Data A d m i n i s t r a t i o n and Data D i c t i o n a r y IMS/VS has been d e s i g n e d f o r a c e n t r a l i z e d a d m i n i s t r a t i o n , w i t h the major f a c i l i t i e s under the c o n t r o l of one Data Base A d m i n i s t r a t o r (DBA). However, w i t h the i n f l u x of more u t i l i t i e s 29 \ and the system becoming more complex the DBA j o b can not be done by one person but by a group of p e o p l e who work i n a c o o r d i n a t e d way. S k i l l e d t e c h n i c i a n s a r e r e q u i r e d f o r the c r e a t i o n and maintenance of the IMS/VS l i b r a r i e s . A Data Communication A d m i n i s t r a t o r w i l l be r e q u i r e d t o handle a l l p o l i c i e s and f o r m a t s r e g a r d i n g t e l e c o m m u n i c a t i o n s and t e r m i n a l s s u p p o r t . The DBA d e f i n e s b o t h the g l o b a l p e r s p e c t i v e (DBD) of a Data Base and the u s e r ' s view (PCB's and PSB's). I t i s the f u n c t i o n of the DBA t o e s t a b l i s h an i n t e r f a c e between programs and the p h y s i c a l c h a r a c t e r i s t i c s of the Database. The DBA d e c i d e s the type of a c c e s s s t o r a g e and p h y s i c a l o r g a n i z a t i o n of the Database. He i s r e s p o n s i b l e f o r r u n n i n g most of the u t i l i t i e s c o n cerned w i t h Backup/ R e c o v e r y / R e s t a r t o p e r a t i o n s . IMS/VS p r o v i d e s the DL/1 Test Program t h a t i s used f o r the c r e a t i o n of t e s t Databases. The DBA can compare performance r e l a t e d a s p e c t s b e f o r e d e c i d i n g the f i n a l c o n f i g u r a t i o n of a p r o d u c t i o n Database. I f IMSADF i s a v a i l a b l e , i t can be used i n c o n j u n c t i o n w i t h t h i s program f o r a d d i n g and d e l e t i n g segments i n c e r t a i n p a r t s of the h i e r a r c h y . As mentioned b e f o r e , the DBA a d m i n i s t r a t i o n i s a complex job t h a t u s u a l l y i s performed by a group of p e r s o n s . The Data D i c t i o n a r y (DD) , a s e p a r a t e p r o d u c t , a l l e v i a t e s many of t h e s e c o m p l e x i t i e s . The DD uses the f a c i l i t i e s of IMS/VS, and i t c o n s i s t s of s e v e r a l IMS/VS Databases. These Databases are used to document non-IMS and IMS Data Base Systems. The DD p r o v i d e s commands f o r the p r o d u c t i o n and d i s p l a y i n g of p r i n t e d r e p o r t s c o n t a i n i n g i n f o r m a t i o n about the d a t a i n the Databases. I t can 30 produce s e v e r a l t y p e s of s t r u c t u r e s t a t e m e n t s about d a t a f i l e s , D a t abases, segments, f i e l d s , e t c which can be used f o r d i f f e r e n t p u r p o s e s . For example, i t can produce DBDs and PSBs i n i t s source form. I t can a l s o g e n e r a t e C o b o l , Assembler and PL/1 d a t a s t r u c t u r e s which are s t o r e d i n s p e c i a l OS l i b r a r i e s f o r f u t u r e r e t r i e v a l by a p p l i c a t i o n programs. Performance r e l a t e d u t i l i t i e s a r e o f f e r e d . The DB mo n i t o r and the DC mo n i t o r g a t h e r r e l e v a n t i n f o r m a t i o n about the system. T h i s i n f o r m a t i o n i s used as i n p u t t o the chosen performance u t i l i t y ( i e s ) . These r e p o r t s g i v e i n d i c a t i o n s about the o v e r a l l performance of the system and the s t r u c t u r e of the Databases, and can used t o d e c i d e when a Database needs t o be r e o r g a n i z e d . The MTO p r o v i d e s f o r a dynamic f a c i l i t y f o r c o n t i n u o u s m o n i t o r i n g of the system. I t cn g i v e a d i s p l a y of the c u r r e n t s t a t u s of a l l r e s o u r c e s , and i t can change c o n f i g u r a t i o n a t t r i b u t e s . The MTO can d e t e c t damaged Databases and i n i t i a t e the p r o p e r r e c o v e r y p r o c e d u r e s . S t r e n g t h s 1) The Data D i c t i o n a r y package p r o v i d e s comprehensive r e p o r t i n g f a c i l i t i e s . 2) Many f a c i l i t i e s and u t i l i t i e s a r e a v a i l a b l e f o r c o n t i n u o u s m o n i t o r i n g of the a c t i v i t i e s i n s i d e the system. 31 Weaknesses 1) No b u i l t - i n Data D i c t i o n a r y . 2} No a u t o m a t i c s t o r a g e r e o r g a n i z a t i o n . A new Data Base D e s c r i p t i o n i s needed when the a c c e s s method changes. 3 ) Data D e f i n i t i o n s a re i n c o n v e n i e n t l y s t a t i c . 4) There can be o n l y one DBA f u n c t i o n . T h i s may l e a d t o e x c e s s i v e c e n t r a l i z a t i o n of database c o n t r o l . 5) Macros t h a t implement DBDs and PSBs do not a l l o w v a l i d a t i o n f e a t u r e s . The da t a c o n t e n t s depends on the good f a i t h of a p p l i c a t i o n programmers. 2.7. Data independence and user views The Data independence a t the s t o r a g e l e v e l i s f a i r l y h i g h . Changes i n the a c c e s s method o r t h e p h y s i c a l o r g a n i z a t i o n of a Database r e q u i r e minimum changes i n the r e s p e c t i v e DBDs. I f the a c c e s s method changes then a new DBD g e n e r a t i o n i s needed, but th e s e changes do not a f f e c t the .PSBs or the a p p l i c a t i o n programs. F a c i l i t i e s are p r o v i d e d f o r ch a n g i n g from one a c c e s s method to a n o t h e r w i t h no e f f e c t on the a p p l i c a t i o n programs. As a r e s u l t t h e r e i s complete independence from the u n d e r l y i n g o p e r a t i n g system a c c e s s method used by the system t o r e a c h the d a t a . Changes i n the c o n c e p t u a l view of a Database may r e q u i r e some change i n a p p l i c a t i o n programs or i n t h e i r PSBs. A p p l i c a t i o n programs are r e s t r i c t e d t o whatever i s s p e c i f i e d i n i t s PSB. Some changes i n the Database may a f f e c t the PSB of an 32 a p p l i c a t i o n program and the user view. Changes t o a DBD, l i k e i n s e r t i o n s and/or d e l e t i o n s of segments or f i e l d s i n c e r t a i n p a r t s of the h i e r a r c h y , may r e q u i r e the r e c o m p i l a t i o n and g e n e r a t i o n of new PSB's. A p p l i c a t i o n programs can not d i r e c t l y a c c e s s a Database. User views are implemented u s i n g l o g i c a l Databases. These d e s c r i p t i o n s a r e c o n t a i n e d i n the PSBs of an a p p l i c a t i o n program. User views can r e l a t e t o one or more p h y s i c a l or l o g i c a l Database u s i n g the concept of l o g i c a l c h i l d and l o g i c a l p a r e n t . A Database can o n l y be updated u s i n g t h e s e u s e r v i e w s . •Strengths 1) High degree of independence from the a c c e s s methods and s t o r a g e o r g a n i z a t i o n . 2) User views a l l o w a c c e s s t o one or more d i f f e r e n t d a t a b a s e s . Weaknesses 1) Low degree of d a t a independence f o r user v i e w s . 2) The s t a t i c c o n f i g u r a t i o n r e s t r i c t s the a p p l i c a t i o n program t o whatever i s s p e c i f i e d i n i t s PSB. 2.8. Data Model The h i e r a r c h i c a l model i s used f o r the i m p l e m e n t a t i o n of a l l P h y s i c a l Databases. A p h y s i c a l Database c o n s i s t s of one or more o c c u r r e n c e s of p h y s i c a l database r e c o r d s , each c o n s i s t i n g 33 of one r o o t segment, and z e r o or more dependent segments. Each segment c o n s i s t s of one or more f i e l d s . U s i n g the concept of l o g i c a l c h i l d and l o g i c a l p a r e n t e x t e n s i o n s a r e p r o v i d e d f o r r e l a t i n g two segments i n the same or d i f f e r e n t P h y s i c a l Data Bases. In t h i s way a l i m i t e d network f a c i l i t y i s p r o v i d e d . The d i f f e r e n t t y p e s of r e l a t i o n s and views t h a t can be s p e c i f i e d a r e d e s c r i b e d i n s e c t i o n 1.3. The DBDs and the PSBs a r e implemented u s i n g s t a n d a r d macro assembler i n s t r u c t i o n s and the DBDGEN and the PSBGEN u t i l i t y programs. These macros are f i x e d and do not a l l o w any type of v a l i d a t i o n p r o c e d u r e s or p r e d e f i n e d t y p e s . The c o n t e n t s of a Database a r e the r e s p o n s i b i l i t y of the A p p l i c a t i o n Programmers. Index f a c i l i t i e s a r e p r o v i d e d w i t h a f u l l range of c a p a b i l i t i e s . For HISAM and HIDAM Databases the index p r o v i d e s d i r e c t a c c e s s t o the r o o t segment. Secondary in d e x e s a r e p r o v i d e d f o r a c c e s s i n g a segment w i t h i n a p h y s i c a l or l o g i c a l Database. One of the f i e l d s i n s i d e the r o o t segment i n HISAM and HIDAM Databases i s known as the key which i s unique f o r each o c c u r r e n c e of the p h y s i c a l Database Record. The index i s c o n s t r u c t e d from t h a t key. In the case of a secondary index the key i s c o n s t r u c t e d from the f i e l d which d e f i n e t h a t i n d e x . S t r e n g t h s 1) Good h i e r a r c h i c a l e x t e n s i o n s w i t h the use of L o g i c a l D atabases. 2) Good index f e a t u r e s . 34 Weaknesses 1) H i e r a r c h i c a l s t r u c t u r e . 2) V a r i a b l e l e n g t h segment i s not p o w e r f u l enough t o a l l o w v a r i a b l e l e n g t h f i e l d s . 2.9 Data S t o r a g e There e x i s t f o u r major d a t a o r g a n i z a t i o n s i n IMS/VS. These are the H i e r a r c h i c a l S e q u e n t i a l A c c e s s Method (HSAM), H i e r a r c h i c a l Indexed S e q u e n t i a l Access Method (HISAM), H i e r a r c h i c a l D i r e c t Access Method (HIDAM) and H i e r a r c h i c a l D i r e c t A c cess Method (HIDAM). HSAM/ HISAM, HIDAM and HDAM a r e not a c c e s s methods i n the u s u a l sense. O p e r a t i n g System a c c e s s methods l i k e SAM, ISAM, VSAM, e t c . (mentioned i n 1.2) a r e s o f t w a r e mechanisms t h a t a c t u a l l y cause the t r a n s f e r of d a t a between p e r i p h e r a l s t o r a g e d e v i c e s and computer memory. The l e t t e r s "AM" a t the end of t h e s e acronyms have t r a d i t i o n a l l y s i g n i f i e d "Access Method". In the case of IMS/VS these l e t t e r s d e s c r i b e d a t a o r g a n i z a t i o n s , and they do not t r a n s f e r d a t a . They i n t e r f a c e w i t h the t r u e O p e r a t i n g Systems a c c e s s methods. F i g u r e 2.2 and 2.3 shows the i n t e r f a c e between the " a c c e s s methods" of IMS/VS and the OS a c c e s s methods. F i g u r e 2.2 shows the i n t e r f a c e w i t h non-VSAM a c c e s s methods and F i g 2.3 w i t h VSAM a c c e s s methods. The f o u r b a s i c IMS/VS a c c e s s methods a r e d e s c r i b e d : 3 5 DL/1 HSAM HISAM HDAM HIDAM ; k i i 1 1 < r 1 > SAM BSAM Q'SAM ISAM OSAM OSAM ISAM OSAM OSAM OS Acc e s s Method Data Bases Non VSAM F i g 2.2 A) H i e r a r c h i c a l S e q u e n t i a l A c cess Method (HSAM): a p h y s i c a l database i s implemented u s i n g a s i n g l e d a t a s e t w i t h f i x e d l e n g t h and unblocked segments. The b l o c k s i z e i s e s t a b l i s h e d w i t h the DBD g e n e r a t i o n . The p o s s i b l e o p e r a t i n g system a c c e s s methods t h a t a r e used a r e SAM, BSAM and QSAM. The h i e r a r c h i c a l sequence i s r e p r e s e n t e d by p h y s i c a l c o n t i g u i t y , and each s t o r e d r e c o r d i s imme d i a t e l y f o l l o w e d by i t s s u c c e s s o r i n h i e r a r c h i c a l sequence. I n s e r t i o n s a r e a l l o w e d o n l y w i t h the f i r s t l o a d i n g and i t i s not p o s s i b l e t o pe r f o r m updates and/or d e l e t i o n s . T h i s o r g a n i z a t i o n i s used by OS a c c e s s methods not s u p p o r t e d by VSAM 36 and i s the o n l y a c c e s s method which uses t a p e s . I t s p r i m a r y importance and use i s f o r m a i n t a i n i n g backup c o p i e s or when the p r o c e s s i s c o m p l e t e l y s e q u e n t i a l . DL/1 HSAM HISAM HDAM HIDAM i l l f r Not KSDS KSDS Supp ESDS ESDS ESDS OS Ac c e s s Methods Data Bases VSAM F i g 2.3 B) H i e r a r c h i c a l Indexed S e q u e n t i a l Access Method (HISAM) In t h i s method of o p e r a t i o n the a c t u a l d a t a need not n e c e s s a r i l y be i n a b s o l u t e p h y s i c a l sequence, but an index t o the da t a i s ar r a n g e d i n sequence. Access t o a segment i s th r o u g h a r o o t segment key v i a an i n d e x . S t o r a g e of d e l e t e d segments a r e not r e c o v e r e d u n l e s s t h e r e i s a r e o r g a n i z a t i o n . The p h y s i c a l database can be implemented u s i n g e i t h e r non-VSAM (ISAM/ OSAM) or VSAM (KSDS/ ESDS) d a t a s e t s . -A database r e c o r d i s implemented 37 as a p h y s i c a l l y c o n t i g u o u s s t r i n g of segments i n h i e r a r c h i c a l sequence. Each sequence of segments i s d i v i d e d i n one or more subsequences. The da t a i s n o r m a l l y s t o r e d i n an ISAM data s e t ( a l t e r n a t i v e l y a VSAM Key Sequenced Data S e t , KSDS). I f o v e r f l o w space, i s needed one OSAM (or VSAM E n t r y Sequence Data Set ESDS) i s a l l o c a t e d and the next dependent i s p l a c e d a t the f r o n t . The main use i s f o r a p p l i c a t i o n s t h a t p r o c e s s d a t a s e q u e n t i a l l y . C) H i e r a r c h i c a l Indexed D i r e c t Access Method (HIDAM) The purpose of t h i s i m p l e m e n t a t i o n i s f o r p r o c e s s i n g d a t a both i n s e q u e n t i a l and d i r e c t ways. A p h y s i c a l data base i s implemented as one or more OSAM or VSAM da t a s e t s . The segments of a HIDAM database can be s t o r e d i n d i f f e r e n t l o c a t i o n s r e l a t i v e t o one a n o t h e r . The s t r u c t u r e i s p r e s e r v e d through p h y s i c a l p o i n t e r s c o n t a i n e d i n the segment p r e f i x e s . IMS/VS manages the space a c c o r d i n g t o i n s e r t i o n s and/or d e l e t i o n s . A p r i m a r y index database i s implemented t o p r o v i d e index a c c e s s t o r o o t segments. P o i n t e r s p r o v i d e d i r e c t a c c e s s t o dependent segments. The p r i m a r y use i s f o r a p p l i c a t i o n s which r e q u i r e a p r o c e s s i n g m i x t u r e of s e q u e n t i a l and d i r e c t a c c e s s . Because s t o r a g e o c c u p i e d by d e l e t e d segments i s r e u s a b l e , i t i s adequate f o r Data Bases w i t h l a r g e volumes of i n s e r t / d e l e t e a c t i v i t y . D) H i e r a r c h i c a l D i r e c t A c cess Method HDAM. T h i s i m p l e m e n t a t i o n i s s i m i l a r t o HIDAM and i t p r o v i d e s d i r e c t a c c e s s t o r o o t segments. The d i f f e r e n c e i s t h a t a c c e s s t o the r o o t segment i s done u s i n g a h a s h i n g r o u t i n e and no index d a t a base i s needed. As w i t h HIDAM Databases t h i s o r g a n i z a t i o n p r o v i d e s c a p a b i l i t i e s f o r the reuse of d e l e t e d segments. I t i s used f o r 38 a p p l i c a t i o n s p r o c e s s i n g d a t a randomly and on l i n e . In a d d i t i o n t o the s e b a s i c methods IMS/VS can use o t h e r a c c e s s methods t o p r o v i d e an i n t e r f a c e between non-IMS/VS a p p l i c a t i o n programs and da t a f i l e s of IMS/VS and v i c e v e r s a . These a c c e s s methods a l l o w the easy t r a n s f e r of d a t a from a non IMS/VS environment t o an IMS/VS system and v i c e v e r s a . The G e n e r a l i z e d S e q u e n t i a l Access Method (GSAM) p r o v i d e s a c c e s s s u p p o r t f o r s i m p l e s e q u e n t i a l d a t a s e t s , such as tape f i l e s , s p e c i f i c d a t a s e t s and o t h e r s which a r e n o n - h i e r a r c h i c a l . The Simple H i e r a r c h i c a l Indexed S e q u e n t i a l Access Method (SHISAM) s u p p o r t s r o o t segments o n l y . I t i s used t o p r o c e s s non-DL/1 d a t a s e t s as DL/1 da t a s e t s d u r i n g m i g r a t i o n t o an IMS/VS environment. S t r e n g t h s 1) S e v e r a l a c c e s s methods a r e a v a i l a b l e . 2) A f u l l range of d e v i c e s i s a v a i l a b l e f o r s t o r i n g d a t a . 3) There i s a complete s e t of u t i l i t i e s f o r s t o r a g e r e o r g a n i z a t i o n . P a r t i a l r e o r g a n i z a t i o n i s p o s s i b l e . Weaknesses 1) The l a r g e number of a c c e s s method c h o i c e s may ten d t o c o m p l i c a t e the DBA's j o b . 2) Databases become u n a v a i l a b l e when t h e i r s t o r a g e i s b e i n g r e o r g a n i z e d . 39 2.10. D i s t r i b u t e d Database F a c i l i t i e s The M u l t i p l e System C o u p l i n g (MSC) f e a t u r e , a s e p a r a t e p r o d u c t , p r o v i d e s d i s t r i b u t e d d atabase f a c i l i t i e s between two or more s e p a r a t e IMS/VS i n s t a l l a t i o n s . One database can not be d i s t r i b u t e d i n t o s e v e r a l systems. F a i l u r e of one system does not compromise or a f f e c t the e x e c u t i o n of the o t h e r systems. The MSC f e a t u r e uses the f a c i l i t i e s p r o v i d e d by the SNA (System Network A r c h i t e c t u r e ) f o r most of i t s o p e r a t i o n s . The i n s t a l l a t i o n of the SNA r e q u i r e s the a v a i l a b i l i t y of VTAM f o r most of the t e l e c o m m u n i c a t i o n f a c i l i t i e s . S t r e n g t h s 1) MSC i s w e l l i n t e g r a t e d and does not a f f e c t performance of systems i n v o l v e d . 2.11. E f f i c i e n c y IMS/VS i s the o v e r a l l r e s u l t of a system i n c o n t i n u o u s development. Many of i t s a c t u a l e f f i c i e n c y r e l a t e d f e a t u r e s were d e s i g n e d as o p t i o n a l i n i t s e a r l y r e l e a s e s and/or d i f f e r e n t v e r s i o n s . IMS/VS p r o v i d e s a wide range of t o o l s and u t i l i t i e s f o r c o n t i n u o u s m o n i t o r i n g and r e o r g a n i z a t i o n of the system. The DB monitor c o l l e c t s d ata which i s used by the Data Base M o n i t o r Report P r i n t Program t o produce s e v e r a l e f f i c i e n c y r e l a t e d r e p o r t s . These r e p o r t s c o n t a i n c a t e g o r i e s and summaries of d i f f e r e n t IMS/VS c a l l s t r a c e d a t v a r i o u s l e v e l s of d e t a i l . In ,a 40 s i m i l a r way, the DC mo n i t o r c o l l e c t s i n f o r m a t i o n which i s used as i n p u t t o the Data Communication M o n i t o r Report P r i n t Program which i n t u r n produces r e p o r t s r e l a t e d t o the performance of the DC p a r t . The system c o n t a i n s s e v e r a l u t i l i t i e s f o r r e o r g a n i z i n g a Database and p a r t i a l r e o r g a n i z a t i o n i s a v a i l a b l e . Some u t i l i t i e s a r e a v a i l a b l e f o r d e t e c t i n g when the performance of a Database i s below an a c c e p t a b l e l e v e l . I f the U t i l i t y C o n t r o l F a c i l i t y i s a v a i l a b l e , most r e o r g a n i z a t i o n and r e c o v e r y f u n c t i o n s can be performed i n a semi-automatic form. A Database i s not a v a i l a b l e w h i l e i t s s t o r a g e i s b e i n g r e o r g a n i z e d . There e x i s t o t h e r e f f i c i e n c y r e l a t e d f e a t u r e s , e i t h e r as p a r t of IMS/VS or as o p t i o n a l p r o d u c t s . The o b j e c t i v e of t h e s e p r o d u c t s i s the a l l e v i a t i o n of the Data A d m i n i s t r a t i o n j o b . Among the s e p r o d u c t s and not d i s c u s s e d b e f o r e i s the Database Design A i d , a p r o d u c t which produces s e v e r a l r e p o r t s a c c o r d i n g to i n p u t and p r o c e s s i n g r e q u i r e m e n t s . These r e p o r t s c o n t a i n i n f o r m a t i o n about elements i n the suggested Database, g r o u p i n g of elements i n t o suggested segments, a suggested h i e r a r c h i c a l o r g a n i z a t i o n of the s e segments, and suggested secondary index segments. F a s t P a t h i s another s e p a r a t e p r o d u c t d e s i g n e d t o en a b l e the user t o s e l e c t e i t h e r improved performance f o r s i m p l y s t r u c t u r e d t r a n s a c t i o n s or f u l l f u n c t i o n f o r complex t r a n s a c t i o n s , depending on the r e q u i r e m e n t s of p a r t i c u l a r a p p l i c a t i o n s . The F a s t Path f e a t u r e uses s e l e c t e d d a t a i n one of two o r g a n i z a t i o n s . One, a Main S t o r a g e Database (MSDB) which 41 c o n s i s t s of a r o o t - o n l y f i x e d l e n g t h segment Database t h a t r e s i d e s i n main s t o r a g e . Two, Data E n t r y Data Base (DEDB) which c o n t a i n s r e c o r d s w i t h r o o t segment ty p e s f o r h o l d i n g f i x e d and summary d a t a , and s e q u e n t i a l dependent segment types of the r o o t s , which c o n t a i n d e t a i l i n f o r m a t i o n . The o b j e c t i v e i s t o p r o v i d e f a s t a c c e s s t o s e l e c t e d data by b y p a s s i n g normal p r o c e d u r e s . F a s t Path Databases a r e not a v a i l a b l e t o IMS/VS-DL/1 a p p l i c a t i o n s and v i c e v e r s a . As a wide v a r i e t y of s t o r a g e o r g a n i z a t i o n i s a v a i l a b l e , t h e r e i s a good degree of freedom f o r c h o o s i n g an a c c e s s method. The s e l e c t i o n i s s p e c i f i e d by the DBA a t the time of DBD g e n e r a t i o n . U s u a l l y the .access method depends on the type of o p e r a t i o n s t h a t are supposed t o be performed w i t h t h a t Database. An a c c e s s method can p r o v i d e good performance f o r c e r t a i n t y p e s of o p e r a t i o n s and bad f o r o t h e r s . For example HISAM Databases o f f e r h i g h e f f i c i e n c y f o r s e q u e n t i a l r e t r i e v a l , but s t o r a g e u t i l i z a t i o n i s poor because d e l e t e d segments s t i l l occupy s t o r a g e . T o o l s f o r i m p r o v i n g programming are p r o v i d e d by the IMSADF, which c o n s i s t s of a wide range of r o u t i n e s . A d i s c u s s i o n of IMSADF i s o f f e r e d i n s e c t i o n 2.1. S t r e n g t h s 1) The r e o r g a n i z a t i o n u t i l i t i e s run i n sem i a u t o m a t i c way, r e d u c i n g the JCL g e n e r a t i o n t o a minimum. 42 ,y Weaknesses 1) Some of the e f f i c i e n c y r e l a t e d f a c i l i t i e s , l i k e IMSADF and UCF a r e s e p a r a t e p r o d u c t s . 2.12. Human I n t e r f a c e IMS/VS i t s e l f c o n t a i n s no human i n t e r f a c e s f o r a p p l i c a t i o n s use. I Q F d n t e r a c t i v e Query F a c i l i t y ) i s a s e p a r a t e p r o d u c t t h a t can query IMS/VS Databases. IQF s u p p o r t s a n o n p r o c e d u r a l language and p r o v i d e s a f r i e n d l y i n t e r f a c e f o r non-programmer u s e r s . I t was d e s i g n e d as a query language f o r making i n q u e r i e s and t o p r o v i d e o n - l i n e r e t r i e v a l of d a t a . I t p r o v i d e s a u t o m a t i c f o r m a t t i n g of ou t p u t r e s u l t s . IQF o f f e r s c a p a b i l i t i e s f o r s o r t i n g a c c o r d i n g t o a d e s i g n a t e d f i e l d i n s i d e a segment. IQF does not o f f e r update or r e p l a c e c a p a b i l i t i e s . IMSADF (IMS A p p l i c a t i o n Development F a c i l i t y ) , a n o t h e r s e p a r a t e p r o d u c t p r o v i d e s a s e t of r o u t i n e s f o r immediate use or f o r t he d e v e l o p i n g of more complex programs. IMSADF has been d i s c u s s e d i n s e c t i o n 2.1. Most of the Human I n t e r f a c e p r o d u c t s a r e o p t i o n a l f e a t u r e s . These enhancement p r o d u c t s u s u a l l y r e q u i r e i n t e r f a c i n g w i t h o t h e r IBM p r o d u c t s , which are not w i t h i n the sphere of Data Base Systems Technology. S e v e r a l s o f t w a r e companies o f f e r a d d i t i o n a l p r o d u c t s w i t h easy i n t e r f a c e t o IMS/VS. These a d d i t i o n a l packages become o b s o l e t e , r a t h e r q u i c k l y because as new l e v e l s of IMS/VS a r e r e l e a s e d , some of the f u n c t i o n s a r e absorbed i n t o 43 the IMS/VS u t i l i t i e s , w h i l e o t h e r s see new v e r s i o n s . S t r e n g t h s 1) A complete s e t of e r r o r messages and codes c o v e r i n g almost every s i t u a t i o n . 2) IMS/VS i s i n c o n s t a n t development and new p r o d u c t s can e a s i l y be adapted t o the system. Weaknesses 1) IMSADF r e q u i r e s a d d i t i o n a l p e r s o n n e l f o r maintenance. 2.13. L o c a l Support F a c i l i t i e s IMS/VS i s not an easy system t o i n s t a l l . The i n s t a l l a t i o n i s c a r r i e d out as a c o n s i d e r a b l e s i z e p r o j e c t . The O p e r a t i n g System has t o be s u b j e c t t o some m o d i f i c a t i o n s and a d d i t i o n s b e f o r e IMS/VS can be e x e c u t e d . S m a l l m o d i f i c a t i o n s a r e needed when a new r e l e a s e of e i t h e r the OS or IMS/VS i s i n s t a l l e d . The i n s t a l l a t i o n of new f e a t u r e s may r e q u i r e hardware and s o f t w a r e p r o d u c t s t h a t have no r e l a t i o n w i t h IMS/VS t o be i n s t a l l e d . The IMS/VS. system d e f i n i t i o n c o n s i s t s of the s p e c i f i c a t i o n items such as IMS/VS l i b r a r i e s , d a t a s e t s , b u f f e r p o o l s i z e , Database D e f i n i t i o n s , Programs C o n t r o l B l o c k s , s c r e e n formats and t e r m i n a l d e v i c e and network c h a r a c t e r i s t i c s . P a r t i a l g e n e r a t i o n and t e s t i n g p r o d u c t s a r e o f f e r e d t o a s s i s t i n t h i s p r o c e s s . The manual I n s t a l l a t i o n Guide p r o v i d e s a one s t e p a t a time p r o c e s s f o r the g e n e r a t i o n of the system. T h i s i n s t a l l a t i o n 44 p r o c e s s r e q u i r e s h i g h l y s k i l l e d s o f t w a r e t e c h n i c i a n s . In g e n e r a l each major a p p l i c a t i o n w i l l r e q u i r e a d d i t i o n a l p e r s o n n e l f o r maintenance. The master t e r m i n a l f a c i l i t y p r o v i d e s c a p a b i l i t i e s f o r d i s p l a y i n g o p e r a t i o n a l s t a t u s of IMS/VS and f o r m o n i t o r i n g the p r e s e n t c o n f i g u r a t i o n . The master t e r m i n a l can d y n a m i c a l l y d e t e c t and i n i t i a t e any a c t i v i t y i n s i d e IMS/VS. In t h i s way damaged Databases can be d e t e c t e d and the r e c o v e r y o p e r a t i o n s can be d y n a m i c a l l y i n i t i a t e d . S t r e n g t h s 1 ) The c e n t r a l i z e d c o n t r o l from the master t e r m i n a l a l l o w s an easy c o n t r o l of the system. 2.14. P o r t a b i l i t y IMS/VS runs on IBM/370 machines under o p e r a t i n g systems OS/VS1 or 0S/VS2. The O p e r a t i n g System has t o undergo s p e c i a l p r e p a r a t i o n b e f o r e the DBMS can r u n . IMS/VS depends h e a v i l y on many of the OS f u n c t i o n s f o r c o r r e c t e x e c u t i o n , and i s v e r y d i f f i c u l t t o i s o l a t e the IMS/VS f u n c t i o n s from the OS f u n c t i o n s . However the System a l l o w s c e r t a i n degree of p o r t a b i l i t y . D i f f e r e n t v e r s i o n s of the same o p e r a t i n g system can run IMS/VS w i t h v e r y s m a l l m o d i f i c a t i o n s . There e x i s t s a c e r t a i n degree of d a t a p o r t a b i l i t y between IMS/VS and non IMS/VS d a t a s e t s . In a d d i t i o n t o the f o u r b a s i c t y p e s of s t o r a g e i m p l e m e n t a t i o n (see Data S t o r a g e ) , IMS/VS a l l o w s the f o l l o w i n g t y p e s : SHSAM (Simple HSAM), SHISAM (Simple 45 HISAM) and GSAM ( G e n e r a l i z e d S e q u e n t i a l Access Method). These t h r e e t y p e s of Databases can be a c c e s s e d by bo t h IMS/VS and non-IMS/VS a p p l i c a t i o n programs. These i m p l e m e n t a t i o n s use s t a n d a r d OS/VS a c c e s s methods. They a r e used when IMS/VS a p p l i c a t i o n programs want t o pass some Database d a t a t o non-IMS/VS a p p l i c a t i o n programs or v i c e v e r s a . U t i l i t i e s a r e a v a i l a b l e t o put d a t a (IMS/VS or not) i n t o t h e s e f o r m a t s . S t r e n g t h s 1) Data p o r t a b i l i t y f a c i l i t a t e s the t r a n s f e r of d a t a among both IMS/VS and non-IMS/VS i n s t a l l a t i o n s . Weaknesses 1) The System i s not p o r t a b l e t o o t h e r O p e r a t i n g Systems o u t s i d e the s p e c i f i c l i n e o f f e r e d by IBM. 2) The O p e r a t i n g System has t o undergo some m o d i f i c a t i o n s b e f o r e the DBMS can r u n . 3) The i n s t a l l a t i o n p r o c e s s i s d i f f i c u l t . 4) The DBMS i s w r i t t e n i n Assembler language. 2.15. R e l i a b i l i t y The o n l i n e system i s m o n i t o r e d by the C o n t r o l Program e x e c u t i n g i n the C o n t r o l R e g i o n , which i s an OS Region d e s i g n a t e d f o r t h a t purpose. A p p l i c a t i o n programs run i n d i f f e r e n t OS Regions and they do not i n f l u e n c e each o t h e r . An a p p l i c a t i o n program a t most w i l l be a b l e t o ABEND the r e g i o n 46 where i t i s o p e r a t i n g . The Master T e r m i n a l i s a b l e t o mo n i t o r the e x e c u t i o n of a l l a p p l i c a t i o n programs and t o d e t e c t damaged d a t a b a s e s . IMS/VS has a c l o s e dependence on the performance of the O p e r a t i n g System f o r o v e r a l l r e l i a b i l i t y . E r r o r s i n s i d e the OS tend t o make the DBMS u n a v a i l a b l e . S e v e r a l u t i l i t i e s a r e p r o v i d e d f o r r e c o v e r y and r e s t a r t o p e r a t i o n s and they c o v e r a wide v a r i e t y of s i t u a t i o n s . The macros t h a t implement the DBDs and the PSBs (See Data A d m i n i s t r a t i o n and Data D i c t i o n a r y ) , do not p r o v i d e b u i l t - i n d a t a v a l i d a t i o n f e a t u r e s , nor do they a l l o w the i n c l u s i o n of u s e r - w r i t t e n r o u t i n e s i n t h e i r g e n e r a t i o n . The c o n t e n t s of a Database w i l l depend on the a p p l i c a t i o n programs used f o r t h e i r u p d a t i n g . A l l v a l i d a t i o n p r o c e d u r e s have t o be i n c l u d e d i n t o the programs. S t r e n g t h s 1) Region i s o l a t i o n p r o t e c t s t h e system from a p p l i c a t i o n program e r r o r s . 2) Vendor i s v e r y r e l i a b l e and s t a b l e . Weaknesses 1) O v e r a l l r e l i a b i l i t y i s i n f l u e n c e d by the O p e r a t i n g System. 2) V a l i d a t i o n r o u t i n e s can not be i n c l u d e d i n the Data d e f i n i t i o n . 47 2.16. S e c u r i t y There e x i s t two l e v e l s of s e c u r i t y i n IMS/VS: Data Communication and Database. Data Communication (DC) s e c u r i t y i s implemented u s i n g o p e r a t i n g system f a c i l i t i e s . IMS/VS i n t e r f a c e s w i t h the Resource A c c e s s C o n t r o l F a c i l i t y (RACF) of OS/VS. RACF i s used as a b a s i c t o o l f o r d e f i n i n g and e n f o r c i n g user a u t h o r i z a t i o n and r e s o u r c e p r o t e c t i o n . VSAM password p r o t e c t i o n can a l s o be used as a s e c u r i t y t o o l t o p r o t e c t d a t a s e t s c o n t a i n i n g IMS/VS d a t a . I n i t i a l s e c u r i t y r u l e s a r e s e t up a t IMS/VS g e n e r a t i o n t i m e . Those r u l e s may s u b s e q u e n t l y be m o d i f i e d by the System Maintenance U t i l i t y (SMU) which i s p a r t of the IMS/VS-DC p r o d u c t . R esources t h a t can be c o n t r o l l e d i n c l u d e p h y s i c a l and l o g i c a l t e r m i n a l s , IMS/VS l i b r a r i e s , database f i l e s , IMS/VS C o n t r o l Region s e r v i c e s and s p e c i f i c t r a n s a c t i o n t y p e s . Database (DB) s e c u r i t y i s i n t e g r a t e d i n t o the Program Communication B l o c k (PCB). I t i s s u p p o r t e d u s i n g the s e n s i t i v e segment and s e n s i t i v e f i e l d f e a t u r e s , which d e f i n e the segments and f i e l d s the program can a c c e s s . The s e t of PCBs an a p p l i c a t i o n program r e q u i r e s c o n s t i t u t e i t s Program S p e c i f i c a t i o n B l o c k (PSB). Program s p e c i f i c a t i o n b l o c k s r e s i d e i n the PSB l i b r a r y and a r e under the c o n t r o l of the DBA. DB s e c u r i t y i s i n h e r e n t t o the PSB f a c i l i t y . A l l a p p l i c a t i o n programs r e q u i r e a PSB t o a c c e s s a d a t a b a s e. U n f o r t u n a t e l y , s i n c e PSBs a r e s t a t i c i n n a t u r e , DB s e c u r i t y can be i n c o n v e n i e n t l y s t a t i c as w e l l . 48 One p e c u l i a r consequence of the h i e r a r c h i c a l model i s t h a t d e l e t i o n of a s e n s i t i v e segment i n the h i e r a r c h y w i l l cause d e l e t i o n of a l l i t s c o r r e s p o n d i n g c h i l d r e n r e g a r d l e s s of whether the PSB d e c l a r e s them s e n s i t i v e or n o t . The segment/edit e x i t a l l o w s user w r i t t e n r o u t i n e s f o r the e n c r i p t i o n / d e c r i p t i o n of d a t a s e t s . The Data D i c t i o n a r y p r o d u c t can a l s o be used f o r r e p o r t i n g a c t u a l s t a n d a r d s and p r o c e d u r e s , and s e t t i n g p o l i c i e s . S t r e n g t h s 1 ) I t i s p o s s i b l e t o i n s e r t some-advanced s e c u r i t y f u n c t i o n s . E n c r i p t i o n and d e c r i p t i o n a r e user w r i t t e n r o u t i n e s used w i t h the segment/edit c o m p r e s s i o n e x i t r o u t i n e . 2) The s e c u r i t y system does not impose any s i g n i f i c a n t impact on the DBMS performance. 3) The use of OS/VS f a c i l i t i e s a l l o w s an e x t r a degree of p r o t e c t i o n f o r d a t a s e t s , c o n t a i n i n g the IMS/VS d a t a . 4) There i s good use of the OS/VS s e c u r i t y f a c i l i t i e s (RACF). Weaknesses 1) There i s no s i n g l e s e c u r i t y f u n c t i o n . The DB s e c u r i t y f u n c t i o n s are d i f f e r e n t i n s t y l e from the DC f u n c t i o n s . 2) Database s e c u r i t y i s not dynamic. A new PSB w i l l have t o be g e n e r a t e d when the s e c u r i t y o p t i o n s f o r an a p p l i c a t i o n program r e q u i r e some change. 3) System i s h i e r a r c h i c a l . 49 2 . J _ 7 . S o f t w a r e Q u a l i t y IMS/VS i s w r i t t e n i n Assembler language. At the p r e s e n t t h e r e i s no i n f o r m a t i o n s about some of the most r e l e v a n t a s p e c t s , such as s o f t w a r e m o d u l a r i t y , s t a n d a r d i z a t i o n w i t h i n the DBMS and q u a l i t y of the i n t e r n a l c o n t r o l b l o c k s t r u c t u r e s . 2 . 1 8 . U t i l i t i e s IMS/VS p r o v i d e s a f u l l range of u t i l i t i e s w i t h d i f f e r e n t p u r p o s e s . The u t i l i t i e s can be c l a s s i f i e d i n the f o l l o w i n g groups: a) G e n e r a t i o n u t i l i t i e s : They a r e used t o a s s i s t i n the c r e a t i o n , and maintenance of Data Bases. Among them a r e u t i l i t i e s f o r the g e n e r a t i o n of DBD's, PSBs and ACB's. B) Data Base u t i l i t i e s : Used f o r r e o r g a n i z a t i o n , r e c o v e r y , l o a d i n g and r e l o a d i n g of data bases. C) System Log u t i l i t i e s : Used f o r r e s t a r t , r e c o v e r y and a n a l y s i s of the system l o g d a t a . D) Performance R e p o r t i n g u t i l i t i e s : Used t o mon i t o r the system w i t h d a t a o b t a i n e d from the DB and the DC m o n i t o r s and t o produce performance r e l a t e d r e p o r t s . A l l u t i l i t i e s a r e s t a n d a r d OS/VS j o b s and a r e s u b j e c t t o JCL r u l e s . F a c i l i t i e s i n some u t i l i t i e s a r e p r o v i d e d t o h e l p c o n s t r u c t JCL f o r r u n n i n g or i n v o k i n g o t h e r u t i l i t i e s . Most of the u t i l i t i e s u s u a l l y o p e r a t e on the dat a b a s e . The i n s t a l l a t i o n of a d d i t i o n f e a t u r e s may r e q u i r e 50 a d d i t i o n a l u t i l i t i e s or some complementary r o u t i n e s t o e x i s t i n g ones. S t r e n g t h s 1) The JCL g e n e r a t i o n j o b i s reduced t o a minimum. 2) I t i s p o s s i b l e t o use some of the OS u t i l i t i e s t h a t a re not s p e c i f i c IMS/VS. Weaknesses 1) There e x i s t too many u t i l i t i e s , w i t h not enough i n t e g r a t i o n of the system. 2) . Some u t i l i t i e s o p e r a t e d i r e c t l y on the database f i l e s , by-p a s s i n g normal s e c u r i t y mechanisms. 2.19 IMS/VS Uses and c o s t s IMS/VS i s a system d e s i g n e d t o work i n a wide v a r i e t y of s i t u a t i o n s . The many s e p a r a t e p r o d u c t s t h a t can be added t o i t and are o f t e n needed have made the IMS/VS Data Base environment a vey c o n p l e x one. These a d d i t i o n a l p r o d u c t s , which are sometimes not mentioned i n Data Base t e c h n o l o g y , impose a d d i t i o n a l overhead on the computer environment and o f t e n r e q u i r e the a c q u i s i t i o n of a d d i t i o n a l hardware components. As a consequence the use of the IMS/VS system i s recommended f o r companies t h a t handle l a r g e , as opposed t o s m a l l , amounts of d a t a . The o r i g i n a l d e s i g n of the IMS/VS system c a l l s f o r o n l y one 51 Data Base A d m i n i s t r a t o r . However, the c u r r e n t c o m p l e x i t y of the t a s k s performed by the system c a l l s f o r a Data A d m i n i s t r a t i o n group. T h i s group d e c i d e s what goes i n t o the Data Bases, who a c c e s s e s them and what s h o u l d be the g e n e r a l o r g a n i z a t i o n of the system. The s e r v i c e s of a n o ther Data Base A d m i n i s t r a t o r a r e r e q u i r e d f o r the Data Communication p a r t f a c i l i t i t e s . The t r a i n i n g of a d m i n i s t r a t i v e p e r s o n n e l , s o f t w a r e t e c h n i c i a n s and system programmers can be e x p e n s i v e and i n some cas e s i t may t a k e more than a y e a r . 2.20 IMS/VS A c c o m p l i s h e d O b j e c t i v e s The o b j e c t i v e s p r e s c r i b e d f o r IMS/VS as d e s c r i b e d i n Chapter 1, s e c t i o n 1, have not been a c c o m p l i s h e d e n t i r e l y . However, IMS/VS i s c o n s t a n t l y c h a n g i n g . New d i s c o v e r i e s i n computer t e c h n o l o g y a r e bound t o f i n d t h e i r way i n t o IMS/VS and take the system c l o s e r t o the p r e s c r i b e d g o a l s . The f i r s t o b j e c t i v e , a p p l i c a t i o n program independence from the u n d e r l y i n g d a t a s t o r a g e methods, has been p a r t i a l l y a t t a i n e d . An a p p l i c a t i o n program views the d a t a i n a p a r t i c u l a r way i n d e p e n d e n t l y from the way i n which t h a t d a t a i s s t o r e d . A p p l i c a t i o n programs a c c e s s the Data Base a c c o r d i n g t o s p e c i f i c i n s t r u c t i o n s p r o v i d e d by the Data Base A d m i n i s t r a t o r . No d i r e c t a c c e s s i s a l l o w e d . However, the c o n f i g u r a t i o n of the Program S p e c i f i c a t i o n B l o c k i s s t a t i c i n t h a t i s c o n f i n e d t o the i n s t r u c t i o n s of the Data Base A d m i n i s t r a t o r . Changes i n the Data Base A d m i n i s t r a t o r i n s t r u c t i o n s may c o n s t r a i n and a f f e c t the c u r r e n t A p p l i c a t i o n Program environment i n d i f f e r e n t ways and 52 may r e q u i r e the r e c o m p i l a t i o n of the programs. The r e s t r i c t i o n s d e s c r i b e d above a r e a consequence of the IMS/VS i n i t i a l d e s i g n . T h i s d e s i g n i s p r i m i t i v e by modern s t a n d a r d s . I t c e n t r a l i z e s a l l a d m i n i s t r a t i v e f u n c t i o n s i n the hands of a s i n g l e Data Base A d m i n i s t r a t o r . Some of the s e d e s i g n l i m i t a t i o n s have been overcome through the use of new s e p a r a t e s o f t w a r e p r o d u c t s d e s i g n e d t o be used i n c o n n e c t i o n w i t h the IMS/VS system. The second o b j e c t i v e , p r e s e r v a t i o n of Database and message i n t e g r i t y , has been reached f o r a l a r g e number of s i t u a t i o n s . The Backup r o u t i n e s can be used t o p e r i o d i c a l l y produce c o p i e s of p o r t i o n s or whole Databases as needed. The Recovery r o u t i n e s can p r e v e n t the l o s s of d a t a i n case of a system breakdown. The r e s t a r t r o u t i n e s can. be used t o s t a r t the system a f t e r a shut down. Some of the Backup/ R e c o v e r y / R e s t a r t f u n c t i o n s a r e performed by s e p a r a t e p r o d u c t s d e s i g n e d t o be used i n c o n n e c t i o n w i t h the IMS/VS system. These p r o d u c t s c o n s t i t u t e one of the s t r o n g e s t and most complete p a r t s of IMS/VS. In a d d i t i o n , as they were developed almost i n d e p e n d e n t l y from the main system, t h e s e p r o d u c t s can be o b t a i n e d from s e v e r a l companies. New hardware such as n o n - i n t e r r u p t i b l e power f a c i l i t i e s and warning d e v i c e s can be o b t a i n e d as w e l l . These d e v i c e s p r o v i d e e x t r a p r o t e c t i o n i n the event of power f a i l u r e s or system c r a s h . The t h i r d o b j e c t i v e , an i n t e g r a t e d Database and Data Communication system, has been p a r t i a l l y a t t a i n e d . The Data Communication p a r t (DC) has been c o m p l e t e l y i n t e g r a t e d w i t h i n the system. However, t h i s i n t e g r a t i o n makes i t sometimes 53 d i f f i c u l t t o d i s t i n g u i s h between the f u n c t i o n s performed by each of the two p a r t s . In the c u r r e n t v e r s i o n of the IMS/VS system the Data Communication p a r t i s h e a v i l y dependent on the O p e r a t i n g System and uses many of i t s f a c i l i t i e s f o r message t r a n s a c t i o n h a n d l i n g and s e c u r i t y p u rposes. In a d d i t i o n , the DC p a r t makes the use o f a good number of a d d i t i o n a l p r o d u c t s p o s s i b l e . These a d d i t i o n a l p r o d u c t s a r e used t o o b t a i n f a s t e r -than-normal a c c e s s t o d a t a s e t s and t o e s t a b l i s h Database D i s t r i b u t i o n f a c i l i t i e s . The Data Communication p a r t i s o p t i o n a l i n t h a t i s a pr o d u c t t h a t may or may not be used i n c o n n e c t i o n w i t h the Database p a r t of the IMS/VS system. P r o d u c t s s i m i l a r t o the Data Communication p a r t can be o b t a i n e d from s o f t w a r e companies o t h e r than IBM. These a l t e r n a t e p r o d u c t s can be i n t e g r a t e d t o the DB p a r t i n the same way t h a t the IBM Data Communication p a r t i s i n t e g r a t e d . 54 CHAPTER 3: METHOD EVALUATION T h i s c h a p t e r w i l l d i s c u s s the method we have here used t o a s s e s s the IMS/VS system f a c i l i t i e s . The method was suggested by the Data Base D i s c u s s i o n Group (DBDG) of UBC. S u g g e s t i o n s t o overcome some of the d i f f i c u l t i e s e n c o u n t e r e d when u s i n g the DBDG method w i l l be p r e s e n t e d . 3.1 E v a l u a t i o n C r i t e r i a C hapter 2 p r e s e n t s an assessment of t h e IMS/VS system a c c o r d i n g t o e i g h t e e n Data Base s u b j e c t c a t e g o r i e s ( S e c t i o n s 2.1 t o 2.18) proposed by the Data Base D i s c u s s i o n Group (DBDG) of UBC. These s u b j e c t c a t e g o r i e s o f f e r an e v a l u a t i o n of the system on the b a s i s of i t s main f u n c t i o n s . The c a t e g o r i e s answer a number of q u e s t i o n s posed by the DBDG and thus i d e n t i f y the major s t r e n g t h s and weaknesses of the Data Base system. The IMS/VS e v a l u a t i o n as p r e s e n t e d i n Chapter 2 i n v o l v e d the a p p l i c a t i o n of the DBDG g u i d e l i n e s , and the i n t e r p r e t a t i o n of IMS/VS t e c h n i c a l j o u r n a l s , but i t l a c k e d e x p e r i m e n t a l d a t a . As suggested by the Data Base D i s c u s s i o n Group, the c o n c l u s i o n s drawn i n t h i s study can be t e s t e d by u s e r s of the p r o d u c t . A v e r i f i e d and f i n a l v e r s i o n w i l l be the r e s u l t of t h i s l a s t e f f o r t . In s e a r c h i n g answers t o the DBDG q u e s t i o n s i t was found t h a t the IMS/VS manuals p r o v i d e d e t a i l s about a l l the major f u n c t i o n s of the system. A good d e a l of i n f o r m a t i o n i s r e p e a t e d i n s e v e r a l IMS/VS manuals. However, these manuals l a c k the O p e r a t i n g System f u n c t i o n d e s c r i p t i o n s t o which they o f t e n 55 r e f e r . The P r i m e r manual o f f e r s a v a l u a b l e d e s c r i p t i o n of the IMS/VS main f e a t u r e s . A s m a l l p e r c e n t a g e of DBDG q u e s t i o n s was not answered. Unanswered q u e s t i o n s d e a l t w i t h t o p i c s such as s o f t w a r e q u a l i t y and e f f i c i e n c y , and were d i f f i c u l t t o answer because they a r e r e l a t e d t o the day-to-day o p e r a t i o n of the system. Examples of t o p i c s r e l a t e d t o s o f t w a r e q u a l i t y which were not a s s e s s e d a r e the m o d u l a r i t y and s t a n d a r d i z a t i o n of the r o u t i n e s t h a t conform the system. Examples of t o p i c s r e l a t e d t o e f f i c i e n c y which were not a s s e s s e d a r e the f u n c t i o n s r e l a t e d t o system performance i n a r e a l environment, l i k e response t i m e , d e t e c t i o n of b o t t l e n e c k s , e t c . The method we have used t o e v a l u a t e the IMS/VS system has s e v e r a l s t r o n g p o i n t s , among them: 1 ) I t c o v e r s a wide v a r i e t y of Data Base system f u n c t i o n s . From those r e l a t e d t o the s i m p l e s t a s p e c t s of human i n t e r f a c e s t o those r e l a t e d t o the most s o p h i s t i c a t e d a r c h i t e c t u r a l s t r u c t u r e s 2) The i n t e r r e l a t i o n s between the d i f f e r e n t f u n c t i o n s of a Data Base system can be i d e n t i f i e d and used as a g u i d e by system d e s i g n e r s . For example, t h i s s t u d y c o n c l u d e d t h a t the u t i l i t y f u n c t i o n s of the IMS/VS system have a v e r y p o s i t i v e impact on o t h e r f u n c t i o n s , i m p r o v i n g the o v e r a l l system performance. The g r o u p i n g of the f u n c t i o n s under s t u d y i n s u b j e c t c a t e g o r i e s p r o v i d e s f o r a l o g i c a l d i s t r i b u t i o n of study l o a d among the members of a team p r o j e c t . The method a l l o w s f o r a t e c h n i c a l comparison of s e v e r a l Data Base Systems. The s u b j e c t c a t e g o r i e s can be used as a b a s i s f o r the d e s i g n of any number of s c o r i n g methods. In t h i s way a company t r y i n g t o choose between d i f f e r e n t Data Base Systems can b e n e f i t from t h i s method i n r e a c h i n g a d e c i s i o n about which system w i l l s u i t t h e i r needs b e s t . 3) 4) In the same way, some weaknesses of the method can be 56 i d e n t i f i e d . 1) R e s e a r c h e r s need t o c o n t i n u o u s l y v e r i f y t h e i r c o n c l u s i o n s t h r o u g h d a t a o b t a i n e d by w o r k i n g on a day-to-day b a s i s w i t h the Data Base System which i s b e i n g e v a l u a t e d . The f u l f i l l m e n t of t h i s need i s not a d e q u a t e l y p r o v i d e d f o r by the method. The method as i t c u r r e n t l y s t a n d s d i v i d e s the assessment p r o c e s s i n two p a r t s t o be c a r r i e d out one a f t e r the o t h e r : an a n a l y t i c a l p a r t based on b i b l i o g r a p h i c r e s e a r c h , and a p r a c t i c a l p a r t t h r o u g h which the c o n c l u s i o n s of the f i r s t p a r t a r e v e r i f i e d . T h i s s e p a r a t i o n has a l s o proven t o be v e r y time and e f f o r t consuming when d e a l i n g w i t h a complex system such as IMS/VS. 2) The s t u d y does not p r o v i d e d f o r the complete e v a l u a t i o n of f u n c t i o n s l i n k e d t o or performed by the O p e r a t i n g System. R e s e a r c h e r s can o n l y a d e q u a t e l y a n a l y s e t h e s e f u n c t i o n s i f t h ey t h r o u g h l y u n d e r s t a n d the f u n c t i o n i n g of the O p e r a t i n g System i t s e l f . For example, our study of IMS/VS f u n c t i o n s i n c l u d e s o n l y p a r t i a l e v a l u a t i o n s of those f u n c t i o n s l i n k e d or performed by the O p e r a t i n g System. 3) Emphasis i s p l a c e d i n i n v e s t i g a t i n g how f u n c t i o n s a r e p e r f ormed. There i s no r e q u i r e m e n t , however, t o d e t e r m i n e the reasons f o r the use of a p a r t i c u l a r a l g o r i t h m i n i mplementing an s p e c i f i c f u n c t i o n . 3.2 Some Recommendations In s e c t i o n 3.1 we t a l k e d about some weaknesses of the Data Base D i s c u s s i o n Group method on which t h i s IMS/VS assessment was based. These weaknesses can be overcome as f o l l o w s : 1 ) The need t o c o n t i n u o s l y v e r i f y c o n c l u s i o n s b e i n g drawn d u r i n g the a n a l y t i c a l p r o c e s s can be f u l f i l l e d by d o i n g the a n a l y s i s and the v e r i f i c a t i o n of the c o n c l u s i o n s s i m u l t a n e o u s l y . ' The work c o u l d be c a r r i e d out i n c o n s t a n t communication w i t h u s e r s . 2) An u n d e r s t a n d i n g of how the host computer ( O p e r a t i n g System) o p e r a t e s can be a c h i e v e d i n two ways: a) making s u r e t h a t the team p r o j e c t i n c l u d e s someone f a m i l i a r w i t h the 57 Operating System terminology as used with the Data Base System; b) working at the Data Base i n s t a l l a t i o n s i t e . 3) Valuable insight i n t o the design considerations can be obtained through an interface with the Data Base System being evaluated, and by contacting the o r i g i n a l designers of such system. 58 APPENDIX 1: DETAILED EVALUATION A p p l i c a t i o n Programming F a c i l i t i e s Q u e s t i o n 40: A v a i l a b i l i t y and q u a l i t y of r e p o r t g e n e r a t o r , e i t h e r as p a r t of the DBMS or a d j u n c t t o i t Assessment: Not a v a i l a b l e as p a r t of IMS/VS. R e p o r t s can be ge n e r a t e d u s i n g Cobol programs. GIS/VS an IBM p r o d u c t can be used t o generate r e p o r t s . Q u e s t i o n 45: A v a i l a b i l i t y and q u a l i t y of b u i l t - i n or a d j u n c t f a c i l i t i e s t o a l l o w c o n v e n i e n t development of i n t e r a c t i v e a p p l i c a t i o n s Assessment: U s i n g IMSADF or O n l i n e Program and Job Development System. IMSADF i s the most common use d - a n d i s a s e p a r a t e p r o d u c t which p r o v i d e s a s e t of r o u t i n e s e i t h e r f o r immediate e x e c u t i o n or f o r use as an a i d i n the c o n s t r u c t i o n of more complex programs Mechanisms: The O n l i n e Program and Job Development System i s an IMS/VS DB/DC a p p l i c a t i o n which p r o v i d e s the a b i l i t y t o mod i f y , t e s t and execute OS/VS j o b s from an IBM 3270 d i s p l a y s t a t i o n s u p p o r t e d by the IMS/VS database and Data Communication System . IMSADF p r o v i d e s a g e n e r a l purpose a p p l i c a t i o n e x e c u t i o n program which i s c u s t o m i z e d and completed by the a d d i t i o n of s p e c i f i c a t i o n s ( r u l e s ) and , i f n e c e s s a r y , s p e c i a l programming , IMSADF i s b a s i c a l l y i n t e n d e d f o r c o n v e r s a t i o n a l a p p l i c a t i o n s , but i t a l s o a l l o w s the development of n o n - c o n v e r s a t i o n a l and b a t c h a p p l i c a t i o n programs. I t i n c l u d e s p r e d e f i n e d common f u n c t i o n s ( d i a l o g management, d a t a - a c c e s s , a p p l i c a t i o n l o g i c and a t r a n s a c t i o n - d r i v e r w i t h m e n u - s e l e c t i o n . S t a t i c R u l e s ( a p p l i c a t i o n s e l e c t i o n , k e y f o r m a t i o n , program e x e c u t i o n and d a t a h a n d l i n g ) p l u s Dynamic R u l e s ( Sign-on , a u d i t and message t a b l e s ) complete the a p p l i c a t i o n program R e f e r e n c e s : 14(1.1) , 21 , 15 Q u e s t i o n 46: What languages a r e s u p p o r t e d by the h o s t - l a n g u a g e i n t e r f a c e Assessment: C o b o l , Assembler and PL/I R e f e r e n c e s : 1(1) Q u e s t i o n 84: Whether the r e s u l t of one database query can s u b s e q u e n t l y be q u e r i e d and/or updated Assessment: Not p o s s i b l e w i t h IQF R e f e r e n c e s : 15 Q u e s t i o n 86: How { e l a b o r a t e , complex, p o w e r f u l } the s e l e c t i o n c r i t e r i a can be f o r s e a r c h o p e r a t i o n s Assessment: A l l o w s a g r e a t d e a l of c o m p l e x i t y 59 Mechanisms: A DL/I c a l l may d e a l w i t h one or more segments i n the h i e r a r c h i c a l p a t h , and/or one or more Segment S e a r c h Arguments. A segment name o p t i o n a l l y f o l l o w e d by one or more commands codes and one or more q u a l i f i c a t i o n s t a t e ments i s c a l l e d a Segment Search Argument(SSA). Q u a l i f i c a t i o n s t a t ements c o n s i s t s of a s e t of comparison e x p r e s s i o n s connected by the boolean o p e r a t o r s '*' or '&' f o r 'and' and '+' or '|' f o r o r . A comparison e x p r e s s i o n c o n s i s t of < f i e l d , comparison o p e r a t o r , value> w i t h the f i e l d b e l o n g i n g t o the segment and the comparison o p e r a t o r b e i n g one of =, <=, >=, =,<,>. There i s no l i m i t on the number of q u a l i f i c a t i o n s t a t ements i n an SSA, but the maximum s i z e of an SSA i s 256,000 b y t e s . Commands codes are s p e c i f i e d by a s i n g l e c h a r a c t e r preceded by an *. There e x i s t 9 commands codes and they a r e used t o modify the way of a s e a r c h . For example command D a l l o w s the r e t r i e v a l of the e n t i r e h i e r a r c h i c a l p a t h up t o the l o w e s t segment s p e c i f i e d i n the DL/I c a l l , the F command a l l o w s the s e a r c h t o s t a r t w i t h the f i r s t o c c u r r e n c e of the segment type i n d i c a t e d under i t s p a r e n t . Command codes can be combined t o make the s e a r c h more p o w e r f u l . In a d d i t i o n IQF a l l o w s complex s e a r c h s a l l o w i n g l o g i c a l , a r i t h m e t i c and r e l a t i o n a l o p e r a t o r s . U s i n g t h i s f a c i l i t i e s i n f o r m a t i o n of one f i e l d can be r e l a t e d t o the c o r r e s p o n d i n g one i n a n o t h e r f i e l d , and even a r i t h m e t i c o p e r a t i o n s can be performed R e f e r e n c e s : 2 9 ( 1 5 ) , 3 ( 6 ) , 6 ( 2 ) , 31 Q u e s t i o n 150: A v a i l a b i l i t y and q u a l i t y of b u i l t - i n s o r t f e a t u r e s Assessment: In g e n e r a l t h e r e i s no b u i l t - i n f e a t u r e s a v a i l a b l e . However, COBOL language f a c i l i t i e s a r e a v a i l a b l e f o r easy s o r t i n g . In a d d i t i o n and f o r query p r o c e s s i n g IQF o f f e r s a sort-merge o p t i o n s f o r t h e r e t r i e v a l of segments. D u r i n g the r e o r g a n i z a t i o n of a Database and u s i n g the Data Base R e o r g a n i z a t i o n u t i l i t y , i t i s p o s s i b l e t o r e f e r e n c e the s o r t o p t i o n s of the OS/VS. I f no o p t i o n s are s p e c i f i e d OS/VS w i l l use d e f a u l t opt i o n s R e f e r e n c e s : 6 ( 5 ) , 31 Q u e s t i o n 154: Degree t o which the DBMS c o n s t r a i n s the normal a p p l i c a t i o n programming environment, e.g. whether programs need s p e c i a l e n t r y sequences, whether they must be i n s p e c i a l l i b r a r i e s , whether c e r t a i n language f e a t u r e s cannot be used, whether non-database f i l e s can be a c c e s s e d , .. Assessment: Yes , IMS/VS c o n s t r a i n t s the language environment, by p r o v i d i n g s e v e r a l i n f l e x i b l e r u l e s , and some mandatory names Mechanisms: Each a p p l i c a t i o n program c o n t a i n s the so c a l l e d "DL/I p o r t i o n of the program". The s t r u c t u r e of t h i s p o r t i o n depends on the language b e i n g used, and i s used by IMS/VS t o f i n d the r e q u i r e d PSB and DBD. IMS/VS 60 f e t c h e s them from t h e i r r e s p e c t i v e l i b r a r i e s and l o a d s them i n t o main s t o r a g e . IMS/VS then f e t c h e s and l o a d s the a p p l i c a t i o n program and g i v e s i t c o n t r o l , p a s s i n g the PCB's as a d d r e s s e s . The PCB mask i s d e f i n e d a c c o r d i n g t o the language i n use. A l l f e a t u r e s of the languages can be used R e f e r e n c e s : 3 ( 7 ) , 29(15) Q u e s t i o n 155: G e n e r a l f e a t u r e s of the d a t a m a n i p u l a t i o n language Assessment: DL/I p r o v i d e s the f o l l o w i n g o p e r a t i o n s : r e t r i e v e unique segment (GU), r e t r i e v e the next s e q u e n t i a l segment (GN), r e p l a c e the d a t a i n an e x i s t i n g segment (REPL), d e l e t e the d a t a i n an e x i s t i n g segment (DLET), i n s e r t a new segment (ISRT) .In a d d i t i o n DL/I p r o v i d e s s e r v i c e c a l l s t h a t enable an a p p l i c a t i o n program t o : i d e n t i f y a p o i n t a t which i t may be r e s t a r t e d , r e s t a r t from a s p e c i f i e d c h e c k p o i n t , put user i n f o r m a t i o n on the IMS/VS system l o g , put s e l e c t e d c o n t r o l b l o c k s on the IMS/VS system l o g and o b t a i n v a r i o u s s t a t i s t i c s from DL/I. R e f e r e n c e s : 1 (2 ) Q u e s t i o n 185 Degree t o which a p p l i c a t i o n programs can query the d a t a d e f i n i t i o n d a t a Assessment: No Mechanisms: There a r e no f a c i l i t i e s f o r q u e r y i n g the d a t a d e f i n i t i o n d a t a . The data d e f i n i t i o n d a t a r e s i d e s i n the DBD l i b r a r y and i s under the c o n t r o l of the DBA R e f e r e n c e s : 16(1) 61 A r c h i t e c t u r e , Computing Environment, Parameter L i m i t s , and  M u l t i t h r e a d i n g Q u e s t i o n 8 O p e r a t i n g system f e a t u r e s r e q u i r e d Assessment: IMS/VS runs under the f o l l o w i n g OS/VS c o n f i g u r a t i o n s : OS/VS1 and 0S/VS2 . S e v e r a l o p t i o n a l f e a t u r e s and l i b r a r i e s of the O p e r a t i n g System a r e r e q u i r e d Mechanisms: Some IMS/VS modules r e q u i r e s p e c i a l macros t h a t are r e s i d e n t i n o p t i o n a l OS/VS l i b r a r i e s R e f e r e n c e s : 9(4) Qu e s t i o n 11.1: Nature of the p r o c e s s s t r u c t u r e , b oth i n s i d e the DBMS and i n the a p p l i c a t i o n environment Assessment: IMS/VS i s s t r u c t u r e d as an e x t e n s i o n t o the c a p a b i l i t i e s of OS/VS, and i s c o n s i d e r e d as an OS/VS a u t h o r i z e d program Mechanisms: IMS/VS uses one or more O p e r a t i n g Systems r e g i o n s . The o n l i n e IMS/VS system i s a c o n t r o l program e x e c u t i n g c o n t i n u o s l y i n ah OS/VS r e g i o n c a l l e d the IMS/VS C o n t r o l r e g i o n , which i s s t a r t e d from the o p e r a t o r ' s c o n s o l e . Other r e g i o n s c a l l e d the Dependent Regions can be s t a r t e d e i t h e r from t h e c o n s o l e or from the master t e r m i n a l . The c o n t r o l r e g i o n owns a l l dat a b a s e s t h a t can be a c c e s s e d by o n l i n e a p p l i c a t i o n programs, and i s r e s p o n s i b l e f o r a l l database i n p u t / o u t p u t done by a p p l i c a t i o n programs. A l l DL/I c a l l s a re s e r v i c e d by the c o n t r o l r e g i o n , and i t h a n d l e s a l l communication w i t h the t e r m i n a l s . The dependent r e g i o n s c o n t r o l l e d by the o n l i n e system a re of two t y p e s : a) Message p r o c e s s i n g r e g i o n s t h a t a re used t o execute a p p l i c a t i o n programs i n response t o incoming messages and q u e r i e s . They handle a l l normal o n l i n e programs. They are under the d i r e c t c o n t r o l of the C o n t r o l R e g i o n . T h i s r e g i o n s can c o n t a i n an a p p l i c a t i o n program i n w a i t s t a t e u n t i l a t r a n s a c t i o n i s passed t o i t . b) b a t c h message p r o c e s s i n g r e g i o n s t h a t a r e used f o r o p e r a t o r s c h e d u l e d b a t c h programs t h a t r e q u i r e a c c e s s t o o n l i n e databases.They a re s c h e d u l e d by OS/VS j o b management. In a d d i t i o n t o o n l i n e IMS/VS system b a t c h e x e c u t i o n s of IMS/VS are normal o p e r a t i n g system j o b s . From 2(pp 87) '..The j o b i s i n i t i a t e d by the o p e r a t o r t h r o u g h a j o b re q u e s t t h a t s p e c i f i e s the IMS/VS r e g i o n c o n t r o l l e r module as the program t o be e x e c u t e d , and a l l o c a t e s t o the j o b the data s e t s f o r the IMS/VS d a t a b a s e s t o be a c c e s s e d . The j o b r e q u e s t a l s o s p e c i f i e s , as a parameter t o be passed t o the r e g i o n c o n t r o l l e r , the name of a u s e r - w r i t t e n program t o be run i n t h i s system e x e c u t i o n . When an o p e r a t i n g system, r e g i o n becomes a v a i l a b l e , the job i s sc h e d u l e d f o r e x e c u t i o n . The r e g i o n c o n t r o l l e r i s f e t c h e d from the l o a d module l i b r a r y and g i v e n c o n t r o l ' . The r e g i o n c o n t r o l l o a d s the c o n t r o l b l o c k s d e f i n i n g the 62 user program, PCB's f o r the Databases t o be a c c e s s e d , l o a d s a c t i o n modules r e q u i r e d , l o a d s the user program and t r a n s f e r c o n t r o l t o i t . A f t e r c o m p l e t i o n c o n t r o l i s r e t u r n e d t o the r e g i o n c o n t r o l l e r , which i n t u r n r e t u r n s c o n t r o l t o the OS, ending the j o b . A r e g i o n where a b a t c h e x e c u t i o n runs i s c a l l e d a Batc h R e g i o n . There can be s e v e r a l b a t c h r e g i o n s but da t a b a s e s can be a s s i g n e d o n l y t o one r e g i o n a t a ti m e . R e f e r e n c e s : 30(1),10(1) Q u e s t i o n 12: What c o n v e r s a t i o n a l t e r m i n a l a c c e s s s e r v i c e s , i f any, the DBMS r e q u i r e s from the o p e r a t i n g system, or whether the DBMS r e q u i r e s t e r m i n a l a c c e s s a t the hardware l e v e l Assessment: Access s e r v i c e s p r o v i d e d by the O p e r a t i n g System are r e q u i r e d . The more common methods a re BTAM and VTAM. I f the i n s t a l l a t i o n i s p l a n n i n g t o use the System Network A r c h i t e c t u r e then i t r e q u i r e s VTAM, which w i l l p r o v i d e the a b i l i t y t o a c c e s s o t h e r program p r o d u c t s , o p e r a t i n g .systems programs, and w i l l a l l o w IMS/VS t o enjoy i t s network c a p a b i l i t i e s Mechanisms: Both BTAM and VTAM p r o v i d e s the b a s i c l i n k f o r da t a t r a n s f e r between a t e r m i n a l and an a p p l i c a t i o n program. The i n t e r f a c e t o IMS/VS i s through the Message Format S e r v i c e . R e f e r e n c e s : 22(1) ,21(1) Q u e s t i o n 15: P e r i p h e r a l equipment r e q u i r e m e n t s o t h e r than a u x i l i a r y s t o r a g e , f o r i n s t a n c e , a j o u r n a l - t a p e d r i v e Assessment: R e q u i r e s a t l e a s t one 2400 or 3400 9 - t r a c k tape u n i t . I n c l u s i o n of a d d i t i o n a l f e a t u r e s may r e q u i r e a d d i t i o n a l equipment R e f e r e n c e s : 1(4),6(5) Q u e s t i o n 18: Degree of m u l t i t h r e a d i n g a l l o w e d f o r DBMS a p p l i c a t i o n s Assessment: The maximum number of t e r m i n a l I/O u s e r s t h a t can be u s i n g t e r m i n a l t r a n s a c t i o n s i s 4095 Mechanisms: The SPAREA macro t h a t i s run d u r i n g i n s t a l l a t i o n time d e f i n e s the maximum number of s c r a t c h p a d a r e a s (SPA) to be m a i n t a i n e d by the IMS/VS system. An SPA ar e a i s a work a r e a ( e i t h e r i n main memory or i n a d i r e c t a c c e s s s t o r a g e d e v i c e ) used by IMS/VS t o r e t a i n i n f o r m a t i o n from the a p p l i c a t i o n program a c r o s s i t s e x e c u t i o n . The s i z e of an SPA a r e a m a i n t a i n e d i n main memory can not exceed 32,767 b y t e s . The s i z e of an SPA m a i n t a i n e d i n an a u x i l i a r y d e v i c e can not exceed the t r a c k l e n g t h or 32,767 b i t e s whichever i s l e s s R e f e r e n c e s : 16(7.23), 9.69 Qu e s t i o n 23: Degree t o which DBMS s e c u r i t y uses and/or r e q u i r e s o p e r a t i n g system s e c u r i t y f e a t u r e s Assessment: IMS/VS has b u i l t - i n 63 f e a t u r e f o r f i e l d and segment a c c e s s c o n t r o l , but r e l i e s h e a v i l y on the o p e r a t i n g system f o r o v e r a l l d atabase s e c u r i t y . Mechanisms: O p e r a t i n g System s e c u r i t y f e a t u r e s used i n c l u d e RACF (Resource Access C o n t r o l F a c i l i t y ) t o p r o t e c t system d a t a s e t and /or VSAM d a t a s e t a c c e s s c o n t r o l mechanism t o p r o t e c t VSAM d a t a s e t s . The master t e r m i n a l can e n f o r c e passwords u s i n g OS f a c i l i t i e s . R e f e r e n c e s : 2(6.4) Q u e s t i o n 28 Whether the s e c u r i t y system i s an e s s e n t i a l d e s i g n f e a t u r e of the DBMS or an a d j u n c t t o i t Assessment: Data s e c u r i t y i s b u i l t - i n i n t o IMS/VS-DB. T e r m i n a l and t r a n s a c t i o n s e c u r i t y i s b u i l d i n t o IMS/VS-DC and i s c o n t r o l l e d t h rough f a c i l i t i e s p r o v i d e d by SMU and RACF. Whether DC i s or i s not an e s s e n t i a l f e a t u r e of IMS/VS ' i s a r g u a b l e ' . Mechanisms: Data S e c u r i t y i s l i m i t e d t o the f a c i l i t i e s p r o v i d e d by the l o g i c a l d atabase mechanism, which i s b a s i c t o the IMS/VS-DC hos t program i n t e r f a c e . T e r m i n a l and t r a n s a c t i o n s e c u r i t y i s implemented v i a c o n f i g u r a t i o n o p t i o n s and master t e r m i n a l i m p e r a t i v e s i n IMS/VS DC. R e f e r e n c e s : . 2 ( 4 ) , 3 ( 7 ) Q u e s t i o n 38: E x i s t e n c e and q u a l i t y of a h o s t - l a n g u a g e i n t e r f a c e Assessment: C o b o l , PL/I and Assembler a v a i l a b l e Mechanisms: The program i s c o m p i l e d t h r o u g h the user s e l e c t e d language c o m p i l e r and p l a c e d i n an a p p r o p i a t e program l i b r a r y , a f t e r i t i s l i n k - e d i t e d w i t h the DL/I language i n t e r f a c e modules R e f e r e n c e s : 3(6) Q u e s t i o n 39: Whether or not the query language, r e p o r t g e n e r a t o r , and u t i l i t i e s go through the same (or e s s e n t i a l l y the same) host language i n t e r f a c e as user a p p l i c a t i o n s do Assessment: U t i l i t i e s i n IMS/VS run as s t a n d a r d OS/VS j o b s o p e r a t i n g d i r e c t l y on the dat a b a s e . A l l o t h e r IMS/VS a p p l i c a t i o n f u n c t i o n s use s t a n d a r d IMS/VS r e s o u r c e s f o r d e s c r i b i n g the d a t a , a c c e s s i n g d a t a , and communicating w i t h u s e r s t e r m i n a l s R e f e r e n c e s : 2, 6, 31 Q u e s t i o n 43: A p p l i c a b i l i t y of the DBMS t o both i n t e r a c t i v e and non-i n t e r a c t i v e a p p l i c a t i o n s , and p o r t a b i l i t y of a p p l i c a t i o n programs between the two environments Assessment: Both b a t c h and o n l i n e a v a i l a b l e . B a t c h p r o c e s s i n g i s u s u a l l y performed when the o n l i n e system i s not b e i n g used because i t r e q u i r e s the database i n an e x c l u s i v e mode. See #11.1 A r c h i t e c t u r e R e f e r e n c e s : 3(3) 64 Q u e s t i o n 52: Whether the programs t h a t implement the d a t a d e s c r i p t i o n d a t a are DBMS a p p l i c a t i o n s - - i . e . , whether the d a t a d e s c r i p t i o n d a t a i s i t s e l f a database i n the DBMS. The term " i n t e g r a t e d data d i c t i o n a r y " u s u a l l y r e f e r s t o the case i n which the data d e s c r i p t i o n data i s a d a t a b a s e . Assessment: Not i n t e g r a t e d Mechanisms: The Data Base D e s c r i p t i o n i s a s e r i e s of macro assembler i n s t r u c t i o n s d e s c r i b i n g such t h i n g s as the database o r g a n i z a t i o n , a c c e s s method, segments, f i e l d s i n a database r e c o r d , and r e l a t i o n s h i p s between d i f f e r e n t t y p e s of segments. See #77 R e f e r e n c e s : 2(1) Quest i o n 61.1 Whether m u l t i t h r e a d i n g i s s u p p o r t e d Assessment: Both b a t c h and o n l i n e e x e c u t i o n can be s u p p o r t e d at the same time Mechanisms: They are s u p p o r t e d through f a c i l i t i e s of the O p e r a t i n g Systems r e g i o n s . One of t h e s e r e g i o n s h o l d s the IMS/VS c o n t r o l program w h i l e the o t h e r r e g i o n s , c a l l e d dependent r e g i o n s , a r e a v a i l a b l e f o r o n l i n e or b a t c h e x e c u t i o n . There e x i s t a maximum of 31 dependent r e g i o n s and they can be of 3 k i n d s : a) Message P r o c e s s i n g Region used f o r o n l i n e e x e c u t i o n , b) B a t c h message p r o c e s s i n g r e g i o n used f o r o p e r a t o r - s c h e d u l e d program t h a t r e q u i r e an o n - l i n e database., and c) b a t c h r e g i o n t h a t i s used f o r normal b a t c h o p e r a t i o n s . See 11.1 A r c h i t e c t u r e R e f e r e n c e s : 3 0 ( I ) Q u e s t i o n 79: Format c o n s t r a i n t s on i n d i v i d u a l d ata o b j e c t s — s i z e , t y p e , . . . Assessment: The f o l l o w i n g v a l u e t y p e s a r e p r o v i d e d f o r a d a t a f i e l d : t ype A l l o w e d l e n g h t ( b y t e s ) Hexadecimal 1-255 C h a r a c t e r 1-255 Packed d e c i m a l 1-16 The more complex s t r u c t u r e s are formed u s i n g the segment concept or a u x i l i a r y ones through the f a c i l i t i e s p r o v i d e d by t h e h o s t language R e f e r e n c e s : 30(11) Q u e s t i o n 80 Maximum number of databases per copy of the DBMS Assessment: A maximum of 5000 databases can be under the c o n t r o l of IMS/VS o n l i n e c o n t r o l program.The DATABASE macro statement s p e c i f i e s a l l databases t o be used under the c o n t r o l of IMS/VS o n l i n e c o n t r o l program Mechanisms: one DATABASE macro i n s t r u c t i o n must be s p e c i f i e d f o r each HSAM, HISAM and HDAM d a t a b a s e s . Two database macro s t a t e m e n t s are r e q u i r e d f o r a HIDAM database : one f o r the index DBD and the o t h e r f o r the HIDAM DBD. One database macro i n s t r u c t i o n must be i n c l u d e d f o r each 65 secondary index database t h a t r e f e r s t o any database d e f i n e d t o the o n l i n e system R e f e r e n c e s : 9 Q u e s t i o n 81: Maximum s t o r a g e s i z e of a database Assessment: A p p a r e n t l y no r e s t r i c t i o n Q u e s t i o n 82 Maximum number of u s e r s t h a t the DBMS can r e c o r d Assessment: There i s a maximun of 5000 p h y s i c a l t e r m i n a l s t h a t can be a t t a c h e d t o the o n l i n e IMS/VS i n s t a l l a t i o n . A p h y s i c a l t e r m i n a l can have a t t a c h e d any number of l o g i c a l t e r m i n a l s . The maximun number of l o g i c a l t e r m i n a l s i s 5000 R e f e r e n c e s : 16(7) Q u e s t i o n 83 Maximum c o m p l e x i t y of a d a t a d e f i n i t i o n , e.g. max. number of da t a o b j e c t s per d a t a d e f i n i t i o n , max. number of d a t a r e l a t i o n s h i p s per da t a d e f i n i t i o n , . . . Assessment: The r o o t may c o n t a i n any number of c h i l d segments t y p e s and each c h i l d any number of c h i l d segment typ e s . T h e r e i s a maximum of 15 segment ty p e s i n any one d i r e c t i o n a l h i e r a r c h i c a l p a t h and a maximum of 255 segment t y p e s f o r a. complete- PDBR. A maximum of 1000 f i e l d s can be d e f i n e d f o r a l l segments i n a DBD and a maximum of 255 f i e l d s can be d e f i n e d f o r any segment type R e f e r e n c e s : 1*0 (1 ) , 29 ( 1 3) Q u e s t i o n 124: Range of a p p l i c a t i o n s the DBMS i s d e s i g n e d t o cov e r Assessment: IMS/VS has been implemented as a g e n e r a l purpose system, such t h a t u s e r s can t a i l o r t o s u i t t h e i r r e s p e c t i v e e n v i r o n m e n t s . However, i t i s m a i n l y used i n computer b u s i n e s s r e l a t e d a p p l i c a t i o n s . R e f e r e n c e s : 1(1 ) Q u e s t i o n 126 What d e v i c e s a r e su p p o r t e d f o r database s t o r a g e Assessment: Tape and d i s k Mechanisms: HSAM databases u s u a l l y r e s i d e i n tape and a r e used as backout copy. HISAM, HSAM and HIDAM r e s i d e i n d i s k f o r o n l i n e p r o c e s s i n g . I f the f a s t p a t h f e a t u r e i s i n s t a l l e d then databases can r e s i d e i n c e r t a i n d e s i g n a t e d r e g i o n s of main memory. Q u e s t i o n 136: Degree t o which the DBMS uses o p e r a t i n g system f a c i l i t i e s (as opposed t o degree t o which the DBMS c i r c u m v e n t s those f a c i l i t i e s ) Assessment: IMS/VS as an a u t h o r i z e d program uses OS/VS f a c i l i t i e s r a t h e r than c i r c u n v e n t i n g them 66 R e f e r e n c e s : 9 Q u e s t i o n 140: Degree t o which DBMS and a d j u n c t programs code can be shared among m u l t i p l e a p p l i c a t i o n p r o c e s s e s ( i . e . whether the code i s r e e n t r a n t and, i f so, whether the r e e n t r a n c y can be used t o make the code u s a b l e by more than one p r o c e s s at once) Assessment: DBMS code i s s h a r a b l e Mechanisms: Through f a c i l i t i e s of the O p e r a t i n g System R e f e r e n c e s : 3(3) Q u e s t i o n 164: Whether the DBMS i n c l u d e s f e a t u r e s t o r e o r g a n i z e i t s own s t o r a g e , or whether s t o r a g e r e o r g a n i z a t i o n i s ac c o m p l i s h e d by a d j u n c t programs Assessment: U t i l i t y C o n t r o l F a c i l i t y p r o v i d e s a semiautomatic way of r e o r g a n i z a t i o n Mechanisms: UCF i s ex e c u t e d as a s t a n d a r d OS/VS j o b . I t r e q u i r e s a JOB c a r d ( p r o v i d e d by i n s t a l l a t i o n ) , EXEC statements and DD st a t e m e n t s t h a t a r e used t o d e f i n e the i n p u t s and o u t p u t s t h a t a r e r e q u i r e d R e f e r e n c e s : 6 ( 7 ) , 18(1) Q u e s t i o n 165: Whether a database i s a v a i l a b l e w h i l e i t s s t o r a g e i s b e i n g r e o r g a n i z e d Assessment: When a r e o r g a n i z a t i o n i s t a k i n g e f f e c t the database i s unloaded and hence not a v a i l a b l e R e f e r e n c e s : 6(5) Q u e s t i o n 166: Whether the DBMS uses the host o p e r a t i n g system's f i l e system, or whether the DBMS has i t s own f i l e system Assessment: I t uses the s t a n d a r d OS/VS f i l e system Q u e s t i o n 168 How and when the DBMS uses i n t e r m e d i a t e , t r a n s i e n t f i l e s Assessment: No Mechanisms: As s p e c i f i e d i n #18 IMS/VS uses SPA a r e a s t o do i n t e r m e d i a t e work. T y p i c a l c o n t e n t of an SPA a r e da t a a v a i l a b l e from the t e r m i n a l and from d a t a b a s e s , t h a t a re saved f o r c o n t i n u i n g the c o n v e r s a t i o n . IMS/VS a u t o m a t i c a l l y compress and expands s c r a t c h p a d c o n t e n t t o reduce d a t a movement and I/O r e q u i r e m e n t s R e f e r e n c e s : 1 ( 2 ) , 1 0 ( 1 ) , 16(1.1) Quest i o n 172: Degree t o which the DBMS d e s i g n a l l o w s a f l e x i b l e boundary between hardware and s o f t w a r e f u n c t i o n s Assessment: IMS/VS o p e r a t e s under the c o n t r o l and f a c i l i t i e s of OS/VS and t h e r e i s no c l e a r d i s t i n c t i o n between IMS/VS and the o p e r a t i n g systems Mechanisms: The c o n s o l e o p e r a t o r communicates w i t h the 67 s c h e d u l e r and the s u p e r v i s o r . The s c h e d u l e r i s the p o r t i o n r e s p o n s i b l e f o r a c c e p t i n g and e x e c u t i n g OS/VS commands and JCL s t a t e m e n t s w h i l e the hardware i s c o n t r o l l e d by the s u p e r v i s o r . The OS/VS n u c l e o u s and i t s r e s i d e n t e x t e n s i o n s p r o v i d e the modules, r e s i d e n t a c c e s s methods and s u p e r v i s o r c a l l s when r u n n i n g i n an IMS/VS environment. In OS/VS p r o c e s s g a i n c o n t r o l of the hardware o n l y t h rough the s u p e r v i s o r . The master t e r m i n a l p r o v i d e s c a p a b i l i t i e s f o r IMS/VS s i m i l a r t o t h o s e p r o v i d e d t o OS/VS by the system c o n s o l e R e f e r e n c e s : 5(1) Q u e s t i o n 183: How the DBMS f u n c t i o n i s d i v i d e d i n t e r n a l l y and what each major d i v i s i o n does Assessment: The 2 major components of IMS/VS a r e the Data Base management s e r v i c e s , which b a s i c a l l y s u p p o r t s m u l t i p l e a p p l i c a t i o n s u s i n g a common d a t a b a s e , and the Data Commnunication s e r v i c e s which support m u l t i p l e t e r m i n a l o r i e n t e d a p p l i c a t i o n u s i n g a common d a t a b a s e . The DB management a r e d e s i g n e d t o p r o v i d e support i n : 1) D e s c r i p t i o n of Data Bases, 2 ) C r e a t i o n of Data Bases, 3) Acc e s s t o and maintenance of Data, 4) S h a r i n g of IMS/VS d a t a Bases by m u l t i p l e IMS/VS subsystems,5) R e o r g a n i z a t i o n of .databases, 6) Recovery and r e c o n s t r u c t i o n of d a t a and 7) Ch e c k p o i n t / r e s t a r t f o r DB en v i r o n m e n t s . The Data Communication management s e r v i c e s of IMS/VS p r o v i d e : 1) A p p l i c a t i o n - independent t e r m i n a l management, 2) Input/Output message t r a f f i c h a n d l i n g , 3) T e r m i n a l and Program message s w i t c h i n g 4) Message format s e r v i c e f o r d e v i c e independence, 5) T r a n s a c t i o n i n i t i a t e d s c h e d u l i n g of a p p l i c a t i o n program, 6) C o n v e r s a t i o n a l / i n t e r a c t i v e a p p l i c a t i o n s u p p o r t , 7) D i a g n o s t i c a i d s , 8) System command and c o n t r o l language, 9) r e s o u r c e s e c u r i t y 10) C h e c k p o i n t / r e s t a r t f o r DB/DC environment, 11) D i s p l a y t e r m i n a l p a g i n g , 12.) a u d i o response. Mechanisms: The Data Base management s e r v i c e s a r e o f f e r e d as b a s i c m a t e r i a l i n a component c a l l e d t he Data Base System. The DB management s e r v i c e s i s p r e r e q u i s i t e t o the DC f e a t u r e . When the DB system and the DC are combined they form the the IMS/VS Data Base/ Data Communication (DB/DC) system. A p p l i c a t i o n programs c a l l upon the database and the da t a communication t h r o u g h DL/1. For the most p a r t a p p l i c a t i o n programming use of DB/DC management s e r v i c e s i s independent of t e r m i n a l and s t o r a g e media programming c o n s i d e r a t i o n s . R e f e r e n c e s : 1 (1 ), 1 0 68 Backup/ Recovery/ and Restart Question 1 9 : OS/VS-style checkpoint/restart f a c i l i t i e s , i . e . a b i l i t y to allow orderly suspension and resumption of application processes on request Assessment: IMS/VS supports checkpoint/restart as one of i t s features and is used for checkpoint, shutting down and restarting IMS/VS executions. Checkpoint and restart c a p a b i l i t i e s are provided for both batch and online systems, and IMS/VS can be stopped and restarted at certain i n t e r v a l s . Checkpoints can be spec i f i e d in application programs almost at w i l l . Mechanisms: The master terminal provide a means for entering commands for checkpoint execution and for an orderly termination of the system. The restart command, i s used for system reconstruction after a controlled stop or an emergency stop or when i n t e g r i t y of the database i s in question. To start IMS/VS again the operator instructs 0/S to start IMS/VS. Once IMS/VS are defined, a message is transmitted to the master terminal requesting an indication of the type of re s t a r t , t h i s answer causes the control to pass to the restart f a c i l i t y , which reads the restart data set or system log. It gets the input messages received but not processed or output messages generated but not transmitted during the previous execution. Any other message or job are put back into the respective queues in which they were l e f t at the previous system stop. After that the master terminal i s n o t i f i e d that the restart i s complete and i t can start sending messages to reassume normal processing References: 1 ( 2 ) , 1 8 ( 1 ) , 5 ( 3 ) Question 1 2 7 Ease and computing cost of performing backup operations Assessment: It i s easy using the Data Base Recovery Control Feature. Mechanisms: Recovery and backup related information are automatically recorded in the RECOM data set References: 1 8 ( 1 ) Question 1 4 8 : Whether u s e r - i n i t i a t e d transaction rollback can be done Assessment: Yes. It can be done up to the most recent synchronization point. Two types of possible rollback operations. One, which i s indicated by return code to the application program and the other to terminate the program with an ABEND message References: 3 ( 8 ) Question 1 6 0 : What transaction logging f a c i l i t i e s are provided—whether unprocessed transaction input i s logged, or before- and after-images. If the l a t t e r , whether l o g i c a l or physical 69 images a r e . l o g g e d Assessment: A l l t r a n s a c t i o n s a r e logged on the system l o g ta p e . Both b e f o r e and a f t e r images a r e r e c o r d e d . For r e c o v e r y p u r p o s e s , however, the system l o g tapes a r e not used d i r e c t l y . The Change A c c u m u l a t i o n U t i l i t y i s used t o s e l e c t changed database l o g r e c o r d s from the l o g t a p e s . An image copy of the database i s a l s o c r e a t e d a t user s p e c i f i e d t i m e s . When backup or r e c o v e r y i s r e q u i r e d , the output of the Change A c c u m u l a t i o n U t i l i t y and the image copy a r e used as i n p u t t o the Database Recovery U t i l i t y . R e f e r e n c e s : 6(6) Q u e s t i o n 163: What r e c o v e r y f e a t u r e s a re b u i l t i n t o the DBMS, as opposed t o f e a t u r e s t h a t a r e s u p p o r t e d by a d j u n c t programs. I f r e c o v e r y f e a t u r e s e x i s t , whether they a r e a u t o m a t i c a l l y i n v o k e d Assessment: Data Base Recovery F e a t u r e i s i n c l u d e d w i t h i n the system Mechanisms: IMS/VS Data Base Recovery C o n t r o l F e a t u r e s t o r e s i n f o r m a t i o n about e v e n t s t h a t might a f f e c t r e c o v e r y i n two r e c o v e r y c o n t r o l d a t a s e t s . These VSAM key sequenced Data Sets a re d e s i g n e d t o c o n t a i n i d e n t i c a l i n f o r m a t i o n (one i s the backup f o r the o t h e r ) , and each r e c o v e r a b l e database or p r o c e s s must be i d e n t i f i e d i n t h i s d a t a s e t , b e f o r e any of the a v a i l a b l e u t i l i t i e s f o r r e c o v e r y i s used. The two da t a s e t s a r e c a l l e d the RECON d a t a s e t . DBRC g e n e r a t e s most of the JCL needed t o run the IMS/VS r e c o v e r y u t i l i t i e s . R e f e r e n c e s : 18(1) 70 Communications F a c i l i t i e s Q u e s t i o n 44: A v a i l a b i l i t y and q u a l i t y of b u i l t - i n t e l e c o m m u n i c a t i o n s f e a t u r e s , or i n t e r f a c e ( s ) t o e x t e r n a l t e l e c o m m u n i c a t i o n systems Assessment: BTAM and VTAM a r e o f f e r e d and any of them a r e c o n t r o l l e d by IMS/VS t h r o u g h the Message Format S e r v i c e and the IMS/VS c o n v e r s a t i o n a l P r o c e s s i n g f a c i l i t i e s . I f VTAM i s used the System Network A r c h i t e c t u r e w i l l be a v a i l a b l e t o o . See #12 R e f e r e n c e s : 1, 16(1,7) 71 Concurrency Q u e s t i o n 59 G r a n u l a r i t y of .the l o c k s Assessment: segment t y p e , segment o c c u r r e n c e Mechanisms: 1.) A PCB a s s o c i a t e d w i t h an a p p l i c a t i o n program may s p e c i f y an o p t i o n whereby a l l o c c u r r e n c e s of an e n t i r e segment type a r e l o c k e d i n e x c l u s i v e mode. IMS/VS w i l l not l o a d and i n i t i a t e a program i f i t s PCB e n t r y c o n f l i c t s w i t h t h a t of any program which i s a l r e a d y e x e c u t i n g . Two PCB e n t r i e s c o n f l i c t i f e i t h e r s p e c i f i e s the EXCLUSIVE o p t i o n f o r the same segment t y p e . 2.) A sha r e d l o c k i s a u t o m a t i c a l l y s e t on a segment o c c u r r e n c e when i t i s r e t r i e v e d v i a a GET HOLD o p e r a t i o n . I f the user updates the o c c u r r e n c e , then the l o c k i s a u t o m a t i c a l l y r a i s e d t o an e x c l u s i v e l o c k . IMS/VS a l s o s u p p o r t s shared l o c k s on segment o c c u r r e n c e s which may be e x p l i c i t l y s e t and r e l e a s e d by an a p p l i c a t i o n program. R e f e r e n c e s : 29(24.5) Quest i o n 59.1: D u r a t i o n of l o c k s Assessment: 1.) E x c l u s i v e l o c k s s e t v i a the PCB e n t r y a r e i n e f f e c t f o r the d u r a t i o n of a program. 2.) The shared l o c k g r a n t e d i n response t o a GET HOLD i s n o r m a l l y r e l e a s e d as soon as the segment concerned ceases t o be c u r r e n t , u n l e s s the l o c k has been upgraded t o the e x c l u s i v e l e v e l . B oth shared and e x c l u s i v e l o c k s (not s e t v i a PCB) are r e l e a s e d upon e x e c u t i o n of a c h e c k p o i n t o p e r a t i o n or a t program c o m p l e t i o n . R e f e r e n c e s : 29(24.5) Q u e s t i o n 59.2: Whether both shared (read) and e x c l u s i v e ( w r i t e ) l o c k s a r e p r o v i d e d Assessment: Both a r e p r o v i d e d Mechanisms: see q u e s t i o n s #59 and #59.1 R e f e r e n c e s : 29(24.5) Q u e s t i o n 61: Whether the l o c k p r o t o c o l i s d e a d l o c k - f r e e , o r , i f n o t , whether d e a d l o c k s a r e d e t e c t e d Assessment: Assuming t h a t a program w a i t s i f i t cannot i m m e d i a t e l y o b t a i n a r e q u e s t e d l o c k , the l o c k p r o t o c o l imposed by IMS/VS i s not dea d l o c k f r e e . Deadlock s i t u a t i o n s happen when a r e q u e s t has been t r i e d t o put i n t o the c o r r e s p o n d i n g queue f o r a r e s o u r c e t h a t i s l o c k e d by o t h e r c o n c u r r e n t program. IMS/VS p r o v i d e s dynamic enqueue/dequeue r o u t i n e s t o i n t e r c e p t p o s s i b l e d e a dlock s i t u a t i o n s d u r i n g enqueue p r o c e s s i n g R e f e r e n c e s : 29(24 . 5) , 1'6 ( 3) Q u e s t i o n 61.5 How d e a d l o c k s a r e r e s o l v e d Assessment: Backout f a c i l i t i e s a r e p r o v i d e d 72 Mechanisms: In a de a d l o c k s i t u a t i o n , one of the a p p l i c a t i o n programs i n v o l v e d i n the de a d l o c k i s ab n o r m a l l y t e r m i n a t e d w i t h an s p e c i a l abnormal t e r m i n a t i o n code. The abnormal t e r m i n a t i o n causes the a c t i v i t y of the t e r m i n a t e d program t o be d y n a m i c a l l y backed out t o the most p r e v i o u s s y n c h r o n i z a t i o n p o i n t , and as i t s h e l d r e s o u r c e s a re r e l e a s e d i t a l l o w s o t h e r programs t o c o n t i n u e i t s o p e r a t i o n . DL/1 p r o v i d e s the ROLL command which p e r m i t s a user t o r e q u e s t backout t o the l a s t s y n c h r o n i z a t i o n p o i n t . S t a r t of program, end of program, and c h e c k p o i n t o p e r a t i o n s a re examples of s y n c h r o n i z a t i o n p o i n t s . R e f e r e n c e s : 29(24.5),10 Q u e s t i o n 64: A v a i l a b i l i t y of p r e d i c a t e l o c k i n g , i . e . l o c k i n g on the b a s i s of some s e l e c t i o n c o n d i t i o n Assessment: no R e f e r e n c e s : 29(24.5) Q u e s t i o n 65: Whether the DBMS i s c o n c u r r e n c y s u p p o r t i n g . Assessment: Yes Mechanisms: The DC f e a t u r e p r o v i d e s a so c a l l e d Program I s o l a t i o n f a c i l i t y . A l l a c t i v i t y of a p p l i c a t i o n programs a re i s o l a t e d from each o t h e r r u n n i n g i n the system u n t i l t h a t a p p l i c a t i o n program reaches a s y n c h r o n i z a t i o n p o i n t . The dynamic enqueue/dequeue r o u t i n e enqueues the a f f e c t e d d a t a between s y n c h r o n i z a t i o n p o i n t s . The dynamic l o g modules saves the p r i o r database r e c o r d images between those s y n c h r o n i z a t i o n p o i n t s a l l o w i n g t o d y n a m i c a l l y back out the e f f e c t s of an a p p l i c a t i o n program w i t h o u t a f f e c t i n g the i n t e g r i t y of the database R e f e r e n c e s : 3 0 ( V ) , 16(3) Q u e s t i o n 67: Whether the degree of c o n c u r r e n c y c o n t r o l i s u s e r -s e l e c t a b l e , e.g. whether u s e r s can e l e c t t o r i s k v i e w i n g the d a t a i n an i n c o n s i s t e n t s t a t e i n exchange f o r q u i c k e r or cheaper a c c e s s Assessment: Yes Mechanisms: IMS/VS p e r m i t s s p e c i f i c a t i o n of an o p t i o n i n the PCB ( c a l l e d the READ EXPRESS o p t i o n ) whereby the program i s a l l o w e d t o see uncommitted changes made by ot h e r c o n c u r r e n t programs. Uncommitted changes a r e those which have been made by a program s t i l l i n p r o g r e s s which may be l a t e r backed o u t . The program i s not a l l o w e d t o update uncommitted segments. R e f e r e n c e s : 29(24.5) Q u e s t i o n 68.1: How complex a t r a n s a c t i o n can be ( i . e . no. of da t a o b j e c t s r e f e r e n c e d , no. and type of a c t i o n s performed) 73 Assessment: no l i m i t Mechanisms: T r a n s a c t i o n s can be w r i t t e n i n the same language as b a t c h p r o c e s s i n g programs and they can have the same s t r u c t u r e and c h a r a c t e r i s t i c s as normal programs. The o n l y d i f f e r e n c e i s t h a t the PCB's a r e lo a d e d i n the c o n t r o l r e g i o n when the program i s f i r s t s c h e d u l e d . IMS/VS m a i n t a i n s a p o o l of PCB's r e t a i n i n g as many as p o s s i b l e i n main memory i n o r d e r t o m i n i m i z e a c c e s s t o the PSB l i b r a r y R e f e r e n c e s : 29(24.5),30(V) 74 Data A d m i n i s t r a t i o n and Data D i c t i o n a r y Q u e s t i o n 16: Degree and type of manual d i r e c t - a c c e s s s t o r a g e a d m i n i s t r a t i o n r e q u i r e d Assessment: A l l s t o r a g e a d m i n i s t r a t i o n and m a i n l y r e o r g a n i z a t i o n i s performed u s i n g manual methods. For the g e n e r a l an a p p r o p i a t e r e o r g a n i z a t i o n u t i l i t y has t o be run. See #164 & 167 A r c h i t e c t u r e R e f e r e n c e s : 10(9) Qu e s t i o n 48: Whether t h e r e i s one copy of the d a t a d e f i n i t i o n d ata f o r both d a t a a d m i n i s t r a t i o n and DBMS o p e r a t i o n , or whether the DBMS o p e r a t e s from one copy and data a d m i n i s t r a t i o n i s done u s i n g a n o t h e r . The term " a c t i v e d a t a d i c t i o n a r y " u s u a l l y means t h a t t h e r e i s o n l y one copy Assessment: There e x i s t s 2 c o p i e s of the Data Base D e s c r i p t i o n f o r each d e f i n e d Database Mechanisms: One of the c o p i e s i s the sour c e form, w h i l e the ot h e r i s the o b j e c t form r e s i d i n g i n . t h e DBD l i b r a r y . I f the Data D i c t i o n a r y i s a v a i l a b l e the source copy can be m a i n t a i n e d t h e r e , or the user can inv o k e some f a c i l i t i e s t o produce a source form R e f e r e n c e s : 2 ( 1 ) , 2 7 ( 1 ) Q u e s t i o n 50: Whether the DBMS or the database i n q u e s t i o n must be made t e m p o r a r i l y u n a v a i l a b l e i n o r d e r t o make a d a t a d e f i n i t i o n t ake e f f e c t Assessment: IMS/VS does not need t o become t e m p o r a r i l y u n a v a i l a b l e , but the Database i n q u e s t i o n becomes u n a v a i l a b l e Mechanisms: For each Database t h e r e i s a unique Data Base D e s c r i p t i o n . The DBD are s t a t i c Assembler language macros i n s t r u c t i o n s . T h e y a r e s u b j e c t t o the r u l e s c o n t a i n e d i n OS/VS and DOS/VS VM/370 Assembler Language. A u t i l i t y c a l l e d DBDGEN i s u s u a l l y run when a new DBD or a replacement i s needed. R e f e r e n c e s : 6(1) Qu e s t i o n 53: What da t a a d m i n i s t r a t i o n d a t a i s p a r t of the d a t a d e s c r i p t i o n d a t a Assessment: The source form of a Data Base i s a v a i l a b l e f o r use by the DBA, w h i l e the o b j e c t form i s i n use. Any changes i n the Data D e s c r i p t i o n w i l l r e q u i r e t o generate a replacement o b j e c t form. A p p l i c a t i o n programs and/or PSB's can be a f f e c t e d by such changes. I f the Data D i c t i o n a r y i s i n s t a l l e d and i n use then the DBA can o b t a i n any i n f o r m a t i o n he wants from the DBD and the PSB l i b r a r i e s . The d i c t i o n a r y can produce r e p o r t s f o r him about PSB, DBD and l o g i c a l v i e w s . R e f e r e n c e s : 10,27(1) 75 Q u e s t i o n 54: What a c c e s s and update usage s t a t i s t i c s a r e c o l l e c t e d and what r e p o r t i n g f e a t u r e s f o r them a r e a v a i l a b l e Assessment: DL/I C a l l Summary Report a v a i l a b l e . The database DB m o n i t o r Report P r i n t Program i s an o f f l i n e program t h a t produces s e v e r a l r e p o r t s r e l a t e d w i t h a c t i v i t y i n the system. Among t h e s e i s the DL/I C a l l Summary R e p o r t . The DL/I C a l l Summary Report a r r a n g e d a t a about PCB's used and f o r each PCB the DL/I c a l l f u n c t i o n ( s ) employed. For each c a l l f u n c t i o n i t r e c o r d s the segment a c c e s s e d and the r e t u r n code o b t a i n e d Mechanisms: The DB m o n i t o r Report P r i n t Program use d a t a g a t h e r e d by the DB m o n i t o r on e i t h e r the IMS/VS system l o g or i n a s e p a r a t e d DB m o n i t o r l o g R e f e r e n c e s : 16(9), 2(8) Q u e s t i o n 55: What d a t a s t o r a g e use s t a t i s t i c s a re a v a i l a b l e and what r e p o r t i n g f a c i l i t i e s f o r them e x i s t Assessment: There e x i s t s s e v e r a l u t i l i t i e s a v a i l a b l e . T h e i r use depend m a i n l y on the type of a c c e s s t o the Data Base. For example the Data Base Surveyor u t i l i t y scans a l l or a user s p e c i f i e d p a r t of an IMS/VS HDAM or HIDAM database p r o v i d i n g a r e p o r t d e s c r i b i n g the p h y s i c a l o r g a n i z a t i o n and the f r e e space u t i l i z a t i o n R e f e r e n c e s : 7(5) Q u e s t i o n 77: A v a i l a b i l i t y and q u a l i t y of s p e c i a l t o o l s ( i f any) f o r m a i n t a i n i n g and q u e r y i n g the data d e s c r i p t i o n d a t a Assessment: A s e p a r a t e IBM p r o d u c t , the IMS/VS Data D i c t i o n a r y i s a v a i l a b l e t o h e l p m a i n t a i n and i n d i r e c t l y query the Data D e s c r i p t i o n Data Mechanisms: The IMS/VS Data D i c t i o n a r y m a i n t a i n s an IMS/VS Database of Data D e f i n i t i o n Data. When an a p p l i c a t i o n database i s t o be c r e a t e d or m o d i f i e d , the d a t a D i c t i o n a r y package can be used t o produce the a p p r o p i a t e database or PSB g e n e r a t i o n macros. A l s o v a r i o u s q u e r i e s and r e p o r t s on the Data D i c t i o n a r y ' s database are s u p p o r t e d R e f e r e n c e s : 27 Q u e s t i o n 119: A b i l i t y t o d e f i n e i n the d a t a d e f i n i t i o n u s e r - w r i t t e n d a t a v a l i d a t i o n p r o c e d u r e s Assessment: Not d u r i n g database d e f i n i t i o n . DBD and PSB g e n e r a t i o n are macro assembler i n s t r u c t i o n s w i t h f i x e d r u l e s . Any v a l i d a t i o n p r o c e d u r e has t o be w r i t t e n as a s e p a r a t e r o u t i n e or as p a r t of an a p p l i c a t i o n program. Mechanisms: IMS/VS can g e n e r a t e some e r r o r messages i f operands or parameters o t h e r than those shown f o r each type of database a r e coded, or i f operands or parameters n e c e s s a r y are o m i t t e d or they do not c o r r e s p o n d t o s p e c i f i c a t i o n s of DBD and PSB. 76 R e f e r e n c e s : 2(1) Q u e s t i o n 120: Whether more than one database a d m i n i s t r a t o r can e x i s t , each w i t h h i s or her own s e t of databases Assessment: There e x i s t s o n l y 1 database a d m i n i s t r a t o r f o r the t o t a l i n s t a l a t i o n . The DBA c o n t r o l s Data Base C r e a t i o n , PSB g e n e r a t i o n , Recovery of Data Bases, e s t a b l i s h i n g s e c u r i t y , e t c . Due t o the c o m p l e x i t y of t h i s j o b i t i s most l i k e l y t h a t the DBA i s a group of pers o n s R e f e r e n c e s : (16) Q u e s t i o n 149: A v a i l a b i l i t y and q u a l i t y of b u i l t - i n d a ta v a l i d a t i o n f e a t u r e s Assessment: There i s i n g e n e r a l no b u i l t - i n d a t a v a l i d a t i o n p r o c e d u r e R e f e r e n c e s : 6(1-63) Q u e s t i o n 167: Degree of DBA c o n t r o l over d a t a s t o r a g e s t r u c t u r e s Assessment: There i s a f a i r degree of c o n t r o l of da t a s t o r a g e s t r u c t u r e s . I t i s p o s s i b l e t o r e o r g a n i z e the d a t a s t r u c t u r e and change the a c c e s s method. P a r t i a l r e o r g a n i z a t i o n i s a v a i l a b l e f o r HDAM and HIDAM da t a b a s e s Mechanisms: There e x i s t 10 r e o r g a n i z a t i o n u t i l i t i e s t h a t a r e run as s t a n d a r d OS/VS j o b s . Some of the r e o r g a n i z a t i o n s a r e u n l i k e l y . See # 57 A r c h i t e c t u r e R e f e r e n c e s : 1 ( 2 ) , 6 ( 5 ) Q u e s t i o n 180: How complex a da t a i n t e g r i t y c o n s t r a i n t the DBMS i s c a p a b l e of e n f o r c i n g , e i t h e r by u s e r - w r i t t e n p r o c e d u r e or by b u i l t - i n d a t a v a l i d a t i o n f e a t u r e , e.g. how many d a t a items may be r e f e r e n c e d , whether c o n s t r a i n t s can be s p e c i f i e d over g r e a t e r than one a c t i o n Q u e s t i o n 181: A v a i l a b i l i t y of au t o m a t i c d a t a m o d i f i c a t i o n f u n c t i o n s , e i t h e r by b u i l t - i n f e a t u r e or by u s e r - w r i t t e n p r o c e d u r e , e.g. e n c r y p t i o n / d e c r y p t i o n , c o m p r e s s i o n , e n c o d i n g / d e c o d i n g , f o r m a t t i n g , e t c . Assessment: The segment e d i t / c o m p r e s s i o n f a c i l i t y i s an IMS/VS f u n c t i o n c o n t a i n i n g u s e r e x i t s t h a t a l l o w the user t o encode, e d i t , or compress the da t a p o r t i o n of a v a r i a b l e l e n g t h segment. E n c r y p t i o n i s performed u s i n g user w r i t t e n procedure which i s e n t e r e d a t the segment e d i t / c o m p r e s s i o n e x i t . Mechanisms: Use of the segment e d i t / c o m p r e s s i o n f a c i l i t y i s s p e c i f i e d by segment type on the SEGM statement i n the DBD. The user w r i t e s an e d i t r o u t i n e t h a t a c t u a l l y m a n i p u l a t e s the da t a i n the segment. The IMS/VS f u n c t i o n g i v e s the e d i t r o u t i n e i n f o r m a t i o n about the segment's l o c a t i o n and a s s i s t s i n moving the segment back and f o r t h between the b u f f e r p o o l and the a p p l i c a t i o n program's i / o 77 a r e a . When a segment i s w r i t t e n , i t i s passed t o the e d i t r o u t i n e f o r e n c r y p t i o n b e f o r e b e i n g put i n the d a t a b a s e . The r e v e r s e happens when a segment i s r e a d , w i t h the segment b e i n g d e c r i p t e d by the e d i t program b e f o r e b e i n g sent t o the u s e r . R e f e r e n c e s : 2(4.2,11) Q u e s t i o n 186: Degree t o which subschemas are v a l i d a t e d a g a i n s t the database d e f i n i t i o n , and whether such v a l i d a t i o n can be done a t w i l l Assessment: User views d e f i n i t i o n s a r e c o n t a i n e d i n the PSB l i b r a r y t h a t i s g e n e r a t e d by the DBA. The system checks t h a t i s a " l e g a l " view ( i . e a l l segments and f i e l d s a r e d e f i n e d i n the DBD and t h a t the h i e r a r c h y i s p r e s e r v e d ) . These v a l i d a t i o n s can not be made a t w i l l . R e f e r e n c e s : 16(1) Q u e s t i o n 187: A v a i l a b i l i t y and q u a l i t y of t o o l s t o h e l p the DBA d i s c o v e r the impact of schema changes on (1) the v a l i d i t y of d a t a i n the da t a b a s e , and (2) the v a l i d i t y of e x i s t i n g subschemas Assessment: The Data D i c t i o n a r y (DD) p r o v i d e s a t o o l f o r d e t e c t i n g the i n p a c t of changes i n the Data Base D e s c r i p t i o n over views and on a p p l i c a t i o n programs. Mechanisms: The DD can produce .reports i n d i c a t i n g which PCB's and which programs may be a f f e c t e d due t o changes i n the DBD. The DBA and programmers a r e r e s p o n s i b l e f o r d o i n g the adequate changes R e f e r e n c e s : 2(9) Q u e s t i o n 191: A v a i l a b i l i t y and q u a l i t y of support f o r " t r i g g e r s " , i . e . a p p l i c a t i o n programs t h a t a r e a u t o m a t i c a l l y i n v o k e d when some p r e s p e c i f i e d d a t a c o n d i t i o n a r i s e s Assessment: None a v a i l a b l e d u r i n g database d e f i n i t i o n . However host languages Cobol and PL/I p r o v i d e some f a c i l i t i e s i n t h a t d i r e c t i o n . R e f e r e n c e s : 6(1) Q u e s t i o n 196: A v a i l a b i l i t y of f e a t u r e s t o h e l p the DBA p r e d i c t the • performance impact of proposed d a t a d e f i n i t i o n changes Assessment: Yes Mechanisms: The DBA can choose t o d e v e l o p a t e s t database t o set up s t a n d a r d s f o r the p r o d u c t i o n d a t a b a s e s . I f the IMSADF i s i n s t a l l e d t he DBA w i l l be a b l e t o d y n a m i c a l l y add segments t o a t e s t database and m o n i t o r i t s a c t i v i t y . R e p o r t s can be g e n e r a t e d t o g i v e i n d i c a t i o n s of the a c t u a l performance c h a r a c t e r i s t i c s . R e f e r e n c e s : 2(5) 78 Data Independence and User Views Q u e s t i o n 56: Degree t o which a p p l i c a t i o n programs a r e p r o t e c t e d from changes i n the c o n c e p t u a l model Assessment: There e x i s t a c e r t a i n degree Mechanisms: Use of LDB which a l l o w s segment and f i e l d i s o l a t i o n t h r ough ' s e n s i t i v e ' d e c l a r a t i o n . New segment type may be added at the same l e v e l i n the h i e r a r c h y (not between two l e v e l s ) w h i t h no e f f e c t a t a l l i n a p p l i c a t i o n programs. However, c e r t a i n m o d i f i c a t i o n i n the o r i g i n a l h i e r a r c h y may r e q u i r e c e r t a i n changes t o a p p l i c a t i o n programs or may a f f e c t i t s PSB. V a r i a b l e l e n g t h segments are a l l o w e d . E q u i v a l e n t t o view concept - must be c a r e f u l about d e l e t e s as d e l e t i o n of pa r e n t segment can wipe out c h i l d r e n segments R e f e r e n c e s : 29,6 Qu e s t i o n 57: Degree t o which changes i n the s t o r a g e l e v e l n e c e s s i t a t e changes i n the c o n c e p t u a l l e v e l Assessment: Not much Mechanisms: The DBD i s s t i l l the same w i t h the o n l y d i f f e r e n c e t h a t the a c c e s s method i s changed. A new DBD i s needed w i t h the run of an a p p r o p i a t e u t i l i t y . T r a n s f e r from one s t o r a g e method t o another i s a v a i l a b l e but f o r some ' t r a n s f e r s ' i t i s u n l i k e l y t o be used. From"To HSAM HISAM HDAM HIDAM HSAM X 'OK #3 OK HISAM #1 X #3 OK HDAM #1/2 #2 X #2 HIDAM #1 OK #3 X #1 Used t o p r o v i d e back up copy or when a r e o r g a n i z a t i o n i s t a k i n g e f f e c t #2 new DB l o a d i n h i e r a r c h i c a l sequence #3 Problems w i t h r o o t segment I t would seem t h a t the c o n c e p t u a l l e v e l does not change but a p p l i c a t i o n s may need r e c o m p i l a t i o n R e f e r e n c e s : 1, 6(1,2) Q u e s t i o n 76: A v a i l a b i l i t y and q u a l i t y of support f o r user views of the d a t a . Low q u a l i t y view s u p p o r t o n l y a l l o w s views t o be d e f i n e d on r e s t r i c t e d s u b s e t s of the d a t a , w h i l e h i g h q u a l i t y view support a l l o w s f i e l d s t o be computed from o t h e r f i e l d s and from e x t e r n a l d a t a , and a l l o w s subschema r e c o r d s t o be c o n s t r u c t e d from more than one schema r e c o r d ' s f i e l d s Assessment: A f a i r l y h i g h q u a l i t y of support f o r user view t h r o u g h the use of l o g i c a l Databases t h a t a l l o w s a user d e f i n e d view of the da t a b a s e . In a d d i t i o n i t a l l o w s the c r o s s - r e f e r e n c i n g or i n t e r r e l a t i o n of d a t a w i t h i n two or more p h y s i c a l databases t h r o u g h the concept of l o g i c a l 79 p a r e n t - l o g i c a l c h i l d Mechanisms: I f a l o g i c a l r e l a t i o n s h i p i s g o i n g t o be d e f i n e d then a l o g i c a l DBD has t o be d e f i n e d . Each l o g i c a l DBD i s d e f i n e d i n terms of one or more u n d e r l y i n g p h y s i c a l PBDs, which must a l r e a d y e x i s t s . The macro s t a t e m e n t s a r e e s s e n t i a l l y the same as w i t h the d e f i n i t i o n of the p h y s i c a l DBDs w i t h the e x c e p t i o n of the SEGM and LCHILD s t a t e m e n t s . The SEGM s t a t e m e n t , which d e s c r i b e s a segment - i t s l e n g t h and p o s i t i o n i n h i e r a r c h y - i s expanded t o i n c l u d e the new typ e s of p o i n t e r s . The LCHILD statement i s added t o i n c l u d e the l o g i c a l r e l a t i o n s h i p beteween the segment t y p e s R e f e r e n c e s : 1 0 ( 4 ) , 29(17) 8 0 Data Independence and User Views Quest i o n 76.1: Degree t o which the database can be updated t h r o u g h a user view Assessment: A user view i s implemented t h r o u g h a l o g i c a l d a t a base Mechanisms: T h i s view i s s u p p o r t e d by a PSB b l o c k i n the PSB l i b r a r y . The Data Base w i l l be update t h r o u g h t h i s view, i f the c o r r e s p o n d i n g a u t h o r i z a t i o n s were d e f i n e d i n such PSB. Because of the h i e r a r c h y model d e l e t i o n of a p a r e n t segment w i l l cause the d e l e t i o n of a l l i t s c h i l d r e n r e g a r d l e s s of i f they were d e c l a r e s e n s i t i v e or not i n the PSB R e f e r e n c e s : 29(14),2 81 Data Model Q u e s t i o n 70: Most el e m e n t a r y element of d a t a t h a t the DBMS knows about, i . e . f i e l d , segment, r e c o r d . . . Assessment: The most ele m e n t a r y element of d a t a t h a t IMS/VS knows i s the f i e l d Mechanisms: F i e l d s a r e d e f i n e d d u r i n g database d e f i n i t i o n and a r e p a r t of a segment R e f e r e n c e s : 1(2) Q u e s t i o n 71: R e l a t i o n s h i p s s u p p o r t e d ( 1 : 1 , 1:n, n:m) Assessment: The main r e l a t i o n s u p p o r t e d i s 1:n. L o g i c a l d a t a bases a l l o w s the d e f i n i t i o n of l o g i c a l r e l a t i o n s h i p s betwen 2 p h y s i c a l d a t a b a s e s and hence r e l a t i o n s of type m: n R e f e r e n c e s : 16(1) Q u e s t i o n 72: Whether or not data o b j e c t s can be o r d e r e d , and what o r d e r i n g c r i t e r i a a re p r o v i d e d ( i . e . o r d e r by e n t r y , o r d e r by some dat a v a l u e ) Assessment: There i s an o r d e r p r o v i d e d when one of the d e f i n e d segments has a f i e l d t h a t d e f i n e s a unique key. The o r d e r w i l l be a c c o r d i n g t o the v a l u e of the key f i e l d R e f e r e n c e s : 6(1) Q u e s t i o n 73: Whether d u p l i c a t e d a t a o b j e c t s a r e a l l o w e d , or whether each o b j e c t r e q u i r e s a unique key Assessment: D u p l i c a t e s d a t a o b j e c t s are a l l o w e d and t h a t i s d e f i n e d i n the f i e l d parameter of a segment a t DBD d e f i n i t i o n time R e f e r e n c e s : 6(4) Q u e s t i o n 85: Whether the database a c c e s s o p e r a t i o n s a r e c l o s e d , i . e . whether the output of one o p e r a t i o n i s the same type of o b j e c t as the i n p u t of the o p e r a t i o n Assessment: O p e r a t i o n i s c l o s e d . A p p l i c a t i o n programs r e t u r n a h i e r a r c h i c a l view Mechanisms: IMS/VS m a i n t a i n s a c u r r e n t p o s i t i o n p o i n t e r t h a t can p o i n t t o any segment i n the database. When a GN c a l l i s i s s u e d the c u r r e n t p o s i t i o n p o i n t e r i s advanced t o p o i n t t o the next segment i n h i e r a r c h i c a l sequence. GU s t a t e m e n t s produce a change i n the p o s i t i o n of the c u r r e n t p o i n t e r . F a c i l i t i e s a r e p r o v i d e d f o r m a i n t a i n i n g more than one c u r r e n t p o i n t e r a t the same t i m e . R e f e r e n c e s : 30,6 Q u e s t i o n 87: Whether non-key f i e l d s can be searched by o t h e r than 82 e x h a u s t i v e means Assessment: Non key f i e l d s may be s e a r c h e d u s i n g secondary in d e x e s Mechanisms: A f t e r DL/I has been i n d i c a t e d t h a t a secondary index i s b e i n g used f o r a p a r t i c u l a r segment DL/I w i l l p r o c e s s the segment as though the indexed f i e l d i s the key. Secondary i n d e x e s a r e s p e c i f i e d i n the DBD g e n e r a t i o n of the Database by macros t h a t i n m e d i a t e l y f o l l o w t h a t segment. R e f e r e n c e s : 2(3) Q u e s t i o n 156 Whether f a c i l i t i e s f o r s p e c i f y i n g l i n k a g e s between d a t a o b j e c t s e x i s t so t h a t update of one d a t a v a l u e w i l l cause a u t o m a t i c update of another Assessment: No Mechanisms: An a p p l i c a t i o n program can update o n l y one segment a t a t i m e . The GH p u t s an e x c l u s i v e l o c k i n o n l y one segment a t a t i m e . B e f o r e u p d a t i n g a segment the program has t o put a GH on t h a t segment R e f e r e n c e s : 3(6) Q u e s t i o n 190: Degree of d a t a t y p i n g / d a t a a b s t r a c t i o n a v a i l a b l e , i . e . whether d a t a elements a r e s t r o n g l y ("date", "address") or weakly ( " c h a r a c t e r ( 8 ) , c h a r a c t e r ( 6 0 ) " ) typed Assessment: No degree Mechanisms: A l l macros f o r the d e f i n i t i o n of DBD's and PSB's ar e s u b j e c t t o n o n - f l e x i b l e r u l e s R e f e r e n c e s : 6(1,2) 83 Data S t o r a g e Q u e s t i o n 13: Data s t o r a g e e f f i c i e n c y Assessment: High e f f i c i e n c y w i t h lower f u n c t i o n a l i t y or low e f f i c i e n c y w i t h h i g h e r f u n c t i o n a l i t y Mechanisms: In HSAM da t a b a s e s a l l segments w i t h i n each database r e c o r d a r e p h y s i c a l l y a d j a c e n t i n s t o r a g e . In t h i s way t h e r e i s v i r t u a l l y no added s t o r a g e overhead. I n c o n v e n i e n c e s a r e t h a t segments can o n l y be updated by r e w r i t i n g the whole da t a b a s e . D e l e t e and r e p l a c e o p e r a t i o n s are not a l l o w e d , and i n s e r t i o n i s a l l o w e d o n l y w i t h the i n i t i a l l o a d i n g . HDAM and HIDAM databases p r o v i d e a h i g h f u n c t i o n a l i t y but the s t o r a g e o r g a n i z a t i o n i s not as e f f i c i e n t as i n HSAM because of the need t o m a i n t a i n p o i n t e r s t o s e v e r a l segments. Because of t h i s d a t a t e n d t o be fragmented. The system t r i e s t o i n s e r t segments as c l o s e as p o s s i b l e t o t h e i r h i e r a r c h i c a l l o c a t i o n and d u r i n g d e l e t i o n s s t o r a g e i s r e c l a i m e d . I n HISAM databases d e l e t e d segments s t i l l ocuppy s t o r a g e . R e f e r e n c e s : 2(4) Q u e s t i o n 117: Whether v a r i a b l e - l e n g t h d a t a o b j e c t s r e q u i r e the minimum amount of s t o r a g e n e c e s s a r y t o r e c o r d t h e i r c u r r e n t v a l u e s , or whether they always r e q u i r e some l a r g e r s i z e Assessment: When a v a r i a b l e l e n g t h segment i s i n i t i a l l y l o a d e d , the space used t o s t o r e i t s d a t a p o s i t i o n i s the l e n g t h s p e c i f i e d i n the MINBYTES operand or the l e n g t h s p e c i f i e d i n the s i z e f i e l d whichever i s l a r g e r . I f the space i n the MINBYTES i s l o n g e r , more space i s a l l o c a t e d f o r the segment than i s r e q u i r e d . The a d d i t i o n a l space can be used when e x i s t i n g d a t a i n the segment i s r e p l a c e d w i t h d a t a t h a t i s l o n g e r R e f e r e n c e s : 10 (4) Q u e s t i o n 118: A v a i l a b i l i t y and q u a l i t y of i n d e x i n g f e a t u r e s Assessment: A f u l l range of index f e a t u r e s o f f e r e d . The most im p o r t a n t i s the index database t h a t p r o v i d e s d i r e c t r e f e r e n c e t o p h y s i c a l database by way of t h e i r c o n t e n t Mechanisms: From 2(pp.104) 'The index database i s a degenerate case of a p h y s i c a l d a t a b a s e , i n which the r e c o r d type c o n s i s t s of a s i n g l e ( r o o t ) segment t y p e . The f o l l o w i n g types of index database a r e p r o v i d e d : a) Pr i m a r y index d a t a b a s e s : t h a t p r o v i d e s d i r e c t a c c e s s t o the r e c o r d s of a p h y s c a l d a t a b a s e ( t h e indexed database) by way of the key v a l u e i n the r e c o r d r o o t segments. The index database c o n t a i n s one r e c o r d f o r each r e c o r d of the inde x e d database. T h i s r e c o r d c o n t a i n s t h e key v a l u e from the r o o t segment of the c o r r e s p o n d i n g r e c o r d i n the inde x e d database ( i n d e x e d databases keys must be u n i q u e ) . Each index d a t a base r e c o r d c o n t a i n s a p o i n t e r t o the 84 r o o t segment of the c o r r e s p o n d i n g r e c o r d i n the in d e x e d d a t a b a s e . b) Secondary index d a t a b a s e s : p r o v i d i n g means f o r d i r e c t l y a c c e s s i n g a segment w i t h i n a p h y s i c a l or l o g i c a l database by means of data w i t h i n the segment or w i t h i n some dependent of the segment. A secondary index database c o n t a i n s one r e c o r d f o r each o c c u r r e n c e of the sourc e segment type i n the indexed d a t a b a s e . Each index database r e c o r d c o n t a i n s a s e a r c h f i e l d v a l u e which i s the c o n c a t e n a t i o n of the v a l u e s of up t o f i v e f i e l d s i n the a s s o c i a t e d source segment. The index d a t a base may a l s o c o n t a i n a subsequence f i e l d d e r i v e d from up t o f i v e s o urce segment f i e l d s , up t o f i v e d u p l i c a t e d a t a f i e l d s t a k e n from the source segment( segment t o be ac c e s s e d ) and a r b i t r a r y user m a i n t a i n e d d a t a . The s e a r c h f i e l d and subsequence f i e l d t o g e t h e r s e r v e as the secondary index database r e c o r d key, which may be e i t h e r a unique or a m u l t i p l e key. The purpose of the subsequence f i e l d i s t o p e r m i t the g e n e r a t i o n of unique keys w i t h i n the index d a t a b a s e , even i n the presence of d u p l i c a t e s e a r c h f i e l d s , and thus make the a c c e s s i n g of the. index database more e f f i c i e n t . Index d a t a b a s e s a re a u t o m a t i c a l l y c r e a t e d and m a i n t a i n e d by the system. In a d d i t i o n they may be a c c e s s e d by a p p l i c a t i o n programs i n the same way as p h y s i c a l d a t a b a s e s . The p r o v i s i o n f o r c a r r y i n g d u p l i c a t e d a t a i n secondary indexes i s u s e f u l f o r r a p i d l y a c c e s s i n g f r e q u e n t l y used d a t a . Index databases a r e d e f i n e d i n a manner s i m i l a r t o p h y s i c a l d a t a b a s e s . An LCHILD statement i s used t o d e s i g n a t e the t a r g e t segment t y p e , and the t a r g e t segment type d e f i n i t i o n s p e c i f i e s , t h r o u g h an XDFLD statement the source segment type and s e a r c h f i e l d . At most one p r i m a r y index database and any number of secondary index databases may be a s s o c i a t e d w i t h a p h y s i c a l d a t a b a s e . A l l p h y s i c a l d a t a b a s e s c o n n e c t e d by l o g i c a l r e l a t i o n s h i p , t o g e t h e r w i t h t h e i r a s s o c i a t e d index d a t a b a s e s , c o n s t i t u t e a database group. The d a t a base group i s a s i g n i f i c a n t c o n s t r u c t from an o p e r a t i o n a l p o i n t of view, s i n c e i n g e n e r a l a l l members of a group must be p r e s e n t t o p r o c e s s any one of them'. R e f e r e n c e s : 30(2) Q u e s t i o n 171 Types of s t o r a g e s t r u c t u r e s used f o r database d a t a Assessment: There e x i s t s e v e r a l t y p e s of d a t a s t o r a g e s t r u c t u r e . Mechanisms: There a r e f o u r p r i n c i p a l database a c c e s s methods, each w i t h i t s own s t o r a g e s t r u c t u r e or s t r u c t u r e s . HSAM data b a s e s uses a s i n g l e SAM data s e t w i t h f i x e d l e n g h t u n b l o c k e d r e c o r d s , and the segments a r e s t o r e d i n h i e r a r c h i c a l sequence, i n one or more c o n s e c u t i v e d a t a s e t s . HISAM databases may be implemented on one of two OS/VS a c c e s s method: ISAM/OSAM or VSAM. With the ISAM/OSAM base, a p h y s i c a l database can be implemented as two d a t a s e t s : an ISAM d a t a s e t and an OSAM d a t a s e t . Wit h the VSAM d a t a s e t two d a t a s e t s a r e a l s o used, a Key 85 Sequenced Data Set (KSDS) and an E n t r y Sequenced Data Set (ESDS). In HIDAM d a t a b a s e s , a p h y s i c a l database i s implemented as one or more OSAM or ESDS d a t a s e t s , each of which h o l d s a l l o c c u r r e n c e s of a g i v e n s e t of segment typ e s (Without r e g a r d t o r e c o r d s t r u c t u r e ) . The da t a s e t t h a t h o l d s r o o t segment o c c u r r e n c e s i s c a l l e d the p r i m a r y d a t a s e t and the remainder( o p t i o n a l ) a r e c a l l e d secondary d a t a s e t s , the segments of a r e c o r d a r e i n t e r c o n n e c t e d t hrough p h y s i c a l p o i n t e r s . An a s s o c i a t e d index database p r o v i d e a c c e s s t o r o o t segments i n p r i m a r y d a t a s e t . S t r u c t u r e of HDAM database i s s i m i l a r t o HIDAM database. The o n l y d i f f e r e n c e i s t h a t a hash f u n c t i o n i s p r o v i d e d i n s t e d of an index database t o a c c e s s the r o o t segments or i n terms of HIDAM the p r i m a r y data s e t R e f e r e n c e s : 30(11) Q u e s t i o n 193: How f r e q u e n t l y d a t a s t o r a g e r e o r g a n i z a t i o n i s r e q u i r e d , as a f u n c t i o n of d a t a d e f i n i t i o n c o m p l e x i t y and update f r e q u e n c y Assessment: I t depends on the p a r t i c u l a r type of dat a b a s e s and the most a p p l i c a t i o n programming environment Mechanisms: For HISAN databases r e o r g a n i z a t i o n i s r e q u i r e d when t h e r e were t o o many i n s e r t i o n s and/or d e l e t i o n s such t h a t the h i e r a r c h i c a l s t r u c t u r e i s no l o n g e r m a i n t a i n e d or d e l e t e d segments s t i l l occupy a good p e r c e n t a j e of s t o r a g e . For HD databases r e o r g a n i z a t i o n i s r e q u i r e d when the segments a re t o o much fragmented or when the q u e n t i t y of p o i n t e r s i s a f f e c t i n g the p e r f o r m a n c e . S e v e r a l u t i l i t i e s and f a c i l i t i e s a r e a v a i l a b l e t o h e l p d e c i d e when t o make a r e o r g a n i z a t i o n . R e f e r e n c e s : 16(6) Q u e s t i o n 194: G r a n u l a r i t y of s t o r a g e r e o r g a n i z a t i o n f u n c t i o n s , i . e . degree t o which database s t o r a g e can be r e o r g a n i z e d i n s m a l l independent p a r t s Assessment: Yes Mechanisms: IMS/VS has i n c o r p o r a t e d the P a r t i a l R e o r g a n i z a t i o n U t i l i t y f a c i l i t y t h a t a l l o w s the user t o pe r f o r m r e o r g a n i z a t i o n i n s p e c i f i e d s e t s of d a t a . F a c i l i t i e s a r e p r o v i d e d t o h e l p d e c i d e the range of da t a t o be r e o r g a n i z e d R e f e r e n c e s : 6(5) 86 D i s t r i b u t e d Database F a c i l i t i e s Q u e s t i o n 173: Whether d i f f e r e n t i n v o c a t i o n s of the DBMS, r u n n i n g i n s e p a r a t e , i n t e r c o n n e c t e d computer systems, can communicate w i t h each o t h e r Assessment: In a d d i t i o n t o communication w i t h o t h e r programs and t e r m i n a l s i n an IMS/VS system, a program can communicate w i t h t e r m i n a l s and programs i n o t h e r IMS/VS i n s t a l l a t i o n s Mechanisms: M u l t i p l e System C o u p l i n g (MSC) i s used. MSC e s t a b l i s h l i n k s between 2 or more s e p a r a t e IMS/VS systems. The t e r m i n a l s and t r a n s a c t i o n codes a re d e f i n e d as b e l o n g i n g t o t h a t system. R e f e r e n c e s : 3(6) Q u e s t i o n 174 Degree of da t a s h a r i n g p o s s i b l e among s e p a r a t e , communicating DBMS i n v o c a t i o n s — w h e t h e r whole databases can be s h a r e d , or j u s t d i r e c t o r i e s of some k i n d Assessment: Whole databases may be shared R e f e r e n c e s : 29(24.5) Q u e s t i o n 175: Whether each s i n g l e database must be s t o r e d e n t i r e l y under one DBMS i n v o c a t i o n , or whether a database can be d i s t r i b u t e d p i e c e w i s e under a s e t of communicating DBMS i n v o c a t i o n s Assessment: Each database must be s t o r e d under the d i r e c t c o n t r o l of a s i n g l e IMS/VS i n v o c a t i o n Q u e s t i o n 176: Degree t o which h a v i n g m u l t i p l e i n t e r c o n n e c t e d DBMS i n v o c a t i o n s compromises, confounds, or r e s t r i c t s c o n c u r r e n c y c o n t r o l , compared t o the case i n which t h e r e i s o n l y one DBMS i n v o c a t i o n Assessment: No, each system a c t s i n a s e p a r a t e way. The communication i s th r o u g h a l o g i c a l l i n k Mechanisms: When two c o n f i g u r a t i o n s a r e conn e c t e d by a MSC l i n k , a d e f i n i t i o n of the l i n k must be i n c l u d e d i n the d e f i n i t i o n of both c o n f i g u r a t i o n s . P h y s i c a l l i n k p arameters i n c l u d e name, type and a d d r e s s of the ch a n n e l or l i n e t h a t implement the l i n k R e f e r e n c e s : 30(IV) Q u e s t i o n 178: In a s e t of i n t e r c o m m u n i c a t i n g DBMS i n v o c a t i o n s , degree t o which c a t a s t r o p h i c f a i l u r e of one i n v o c a t i o n a f f e c t s a v a i l a b i l i t y of the o t h e r s Assessment: Each system i n a m u l t i p l e system c o n f i g u r a t i o n m a i n t a i n s i t s own r e c o v e r a b i l i t y and uses the f u l l r e c o v e r y f e a t u r e s of a s i n g l e system. F a c i l i t i e s a r e p r o v i d e d t o back up u n a v a i l a b l e m u l t i s y s t e m s c o n n e c t i o n s 87 and systems Mechanisms: When one of the i n t e r c o n n e c t e d systems f a i l s the l o g i c a l l i n k t o o t h e r systems i s l o s t and a l l communications have t o w a i t u n t i l i t i s s u c c e s s f u l l y r e s t a r t e d on the same or an a l t e r n a t e p h y s i c a l l i n k . R e f e r e n c e s : 5(3) Q u e s t i o n 179: Degree t o which h a v i n g m u l t i p l e i n t e r c o n n e c t e d DBMS i n v o c a t i o n s compromises, confounds, or r e s t r i c t s backup and r e c o v e r y , compared t o the case f o r which t h e r e i s o n l y one DBMS i n v o c a t i o n Assessment: No, h a v i n g m u l t i p l e i n t e r c o n n e c t e d DBMSs does not compromise, confound, or r e s t r i c t backup or r e c o v e r y . Mechanisms: Each system i n the m u l t i s y s t e m c o n f i g u r a t i o n s t i l l use the f u l l r e c o v e r y c a p a b i l i t i e s of IMS/VS. F u l l r e c o v e r y i n the m u l t i s y s t e m c o n f i g u r a t i o n i s ensured as lo n g as no l o g tapes a re l o s t and no c o l d s t a r t of the system i s attem p t e d . R e f e r e n c e s : 10(12), 5(3) 88 Ef f i c i e n c y Q u e s t i o n 2: CPU l o a d imposed as a f u n c t i o n of database s i z e and t r a n s a c t i o n r a t e Assessment: The e f f e c t of the s i z e of the Database on CPU l o a d w i l l m a i n l y depend on the k i n d of o r g a n i z a t i o n used at the s t o r a g e l e v e l . For example i n HISAM d a t a b a s e s , d e l e t e d segments s t i l l ocuppy p h y s i c a l s t o r a g e u n t i l a r e o r g a n i z a t i o n i s performed. For HIDAM and HDAM dat a b a s e s i t w i l l depend depend on the a c t u a l q u a n t i t y of f r a g m e n t a t i o n s a l r e a d y imposed R e f e r e n c e s : 6(5) Q u e s t i o n 4: Amount of p r o c e s s o r memory r e q u i r e d t o s t o r e the DBMS when no database a c t i v i t y i s i n p r o g r e s s ( r e s i d e n c y r e q u i r e m e n t ) Assessment: For a b a s i c support of DC a t l e a s t 500K Mechanisms: The t o t a l amount of s t o r a g e w i l l depend on the t o t a l number of f e a t u r e s r e q u i r e d t o i n s t a l l . IBM thr o u g h c h a p t e r 5 of the Systems Programming Manual p r o v i d e s s e v e r a l f o r m u l a s and g u i d e l i n e s t o c a l c u l a t e the s t o r a g e r e q u i r e d f o r each a d d i t i o n a l f e a t u r e R e f e r e n c e s : 4(5) Q u e s t i o n 90: A v a i l a b i l i t y and q u a l i t y of performance t u n i n g mechanisms Assessment: Yes. Most of the t u n n i n g t o o l s a r e based i n d e t e c t i n g p r o c e s s o r r e s o u r c e problems, I/O r e s o u r c e c o n t e n t i o n , communication performance. Other t u n n i n g t o o l s c o n s i s t of u t i l i t i e s used f o r making a r e o r g a n i z a t i o n of the d a t a base Mechanisms: IMS/VS p r o v i d e s 2 s e p a r a t e m o n i t o r s : The DB monitor and the DC m o n i t o r . Each m o n i t o r g a t h e r and format performance r e l a t e d d a t a and r e c o r d t h i s d a t a on a s t a t i s t i c a l r e p o r t , t h e s e s t a t i s t i c s a r e used or can be used as i n p u t t o r e l a t e d r e p o r t programs, t h a t produces o u t p u t s summarizing and c a t e g o r i z i n g IMS/VS a c t i v i t i e s R e f e r e n c e s : 5 ( 3 ) , 2 ( 8 ) , 1 0 ( 1 0 ) Q u e s t i o n 114: A v a i l a b i l i t y and q u a l i t y of e f f i c i e n c y - i m p r o v i n g f e a t u r e s , e.g. a b i l i t y t o p r e c o m p i l e q u e r i e s , a u t o m a t i c s t o r a g e r e o r g a n i z a t i o n , a u t o m a t i c performance m o n i t o r i n g and t u n i n g , e t c . Assessment: IMSADF a l l o w s many IMS/VS a p p l i c a t i o n s t o be implemented w i t h o u t c o n v e n t i o n a l programming. IMSADF p r o v i d e s f a c i l i t i e s f o r implementing t e s t d a t a b a s e s w i t h dynamic i n s e r t i o n and d e l e t i o n of segments. In t h i s way the DBA can have some g u i d e l i n e s about performance and r e p o r t s t o h e l p him d e c i d e the bes t o p t i o n f o r a p r o d u c t i o n d a t a b a s e . R e o r g a n i z a t i o n or chan g i n g the s t r u c t u r e of s t o r a g e can be a c c o m p l i s h u s i n g some of the 8 9 a v a i l a b l e u t i l i t i e s or w r i t t i n g a program t o such e f f e c t . The U t i l i t y C o n t r o l F a c i l i t y can be used t o p e r f o r m most of the o p e r a t i o n s and m a i n t a i n a n c e f o r both r e c o v e r y and r e o r g a n i z a t i o n i n a semiautomatic way R e f e r e n c e s : 14(1) Q u e s t i o n 157 How e f f i c i e n t the DBMS i s f o r s e q u e n t i a l r e t r i e v a l Assessment: S e v e r a l degrees of e f f i c i e n c y Mechanisms: The most e f f i c i e n t a r e HSAM databases because a l l segments are s t o r e d i n h i e r a r c h i c a l sequence, and s e q u e n t i a l r e t r i e v a l of segments w i l l be easy. The most c o m p l i c a t e d a r e HDAM and HIDAM. In the case of HDAM databases s e q u e n c i a l a c c e s s g e t s c o m p l i c a t e d because of ha s h i n g a c c e s s t o r o o t s and i n the case of HIDAM because of f r a g m e n t a t i o n and t r a v e r s i n g 2 dat a b a s e s R e f e r e n c e s : 29(18) Q u e s t i o n 170: A v a i l a b i l i t y and q u a l i t y of query o p t i m i z a t i o n f e a t u r e s ( i . e . a c c e s s s t r a t e g y c o m p u t a t i o n methods) Assessment: None i n t e g r a t e d . Another IBM p r o d u c t : f a s t p a t h f e a t u r e i s o f f e r e d t o produce f a s t e r response time and i t a l l o w s t e r m i n a l s t o have r a p i d a c c e s s t o main s t o r a g e databases (up t o f i e l d l e v e l ) and t o d i r e c t a c c e s s d a t a e n t r y d a t a b a s e s . The user can choose use t h i s f e a t u r e but he has no c o n t r o l on i t . Mechanisms: F a s t p a t h bypasses the normal IMS/VS t r a n s a c t i o n message queueing and a p p l i c a t i o n s c h e d u l i n g R e f e r e n c e s : 11 90 Human I n t e r f a c e s Q u e s t i o n 37: A v a i l a b i l i t y and q u a l i t y of n a i v e - u s e r - f r i e n d l y query f a c i l i t i e s , e i t h e r as p a r t of the DBMS or a d j u n c t t o i t Assessment: Yes Mechanisms: The I n t e r a c t i v e Query F a c i l i t y ( I Q F ) , a s e p a r a t e p r o d u c t , i s a v a i l a b l e f o r use i n IMS/VS i n s t a l l a t i o n s R e f e r e n c e s : 31 Qu e s t i o n 41: A v a i l a b i l i t y and q u a l i t y of advanced-user query and r e p o r t -g e n e r a t o r f a c i l i t i e s , e.g. f a c i l i t i e s w i t h c o n c i s e e r r o r messages, l e s s p r o m p t i n g , and more p o w e r f u l p r i m i t i v e s Assessment: not a v a i l a b l e , but IQF can be c o n s i d e r e d i n t h i s l i n e R e f e r e n c e s : 31 Quest i o n 42.1: Whether the query and r e p o r t g e n e r a t o r f a c i l i t i e s a r e p r o c e d u r a l or n o n - p r o c e d u r a l Assessment: IQF i s a n o n p r o c e d u r a l f a c i l i t y R e f e r e n c e s : 31 Quest i o n 121: A p p r o p r i a t e n e s s of DBMS f o r s m a l l problems Assessment: IMS/VS i s a l a r g e and complex system t h a t i s not recommended f o r s m a l l problems. Q u e s t i o n 122: G e n e r a l q u a l i t y of user d i a g n o s t i c f e a t u r e s ( e.g. e r r o r messages) Assessment: Good Mechanisms: There e x i s t s a manual on e r r o r codes. Each e r r o r c o n t a i n s a s h o r t d e s c r i p t i o n . The user i s r e f e r r e d t o the manual f o r a more e x t e n s i v e e x p l a n a t i o n and p o s s i b l e a c t i o n R e f e r e n c e s : 13 Qu e s t i o n 146: Whether the query l a n g u a g e ( s ) i n c l u d e update f e a t u r e s Assessment: No Mechanisms: IQF i s a query f a c i l i t y and i t does not c o n t a i n any update f e a t u r e s . IMSADF can be used as a query language f a c i l i t y and as such i n c l u d e update f a c i l i t i e s R e f e r e n c e s : 15(2.9 2.13) , 31 Qu e s t i o n 147: Whether the r e p o r t g e n e r a t o r ( s ) i n c l u d e update f e a t u r e s Assessment: not a v a i l a b l e Q u e s t i o n 153: A v a i l a b i l i t y and q u a l i t y of b u i l t - i n or a d j u n c t ( b a t c h ) d a t a -91 e n t r y f a c i l i t i e s Assessment: Yes Mechanisms: U s u a l l y a c c o m p l i s h e d by user w r i t t e n a p p l i c a t i o n programs t h a t a r e s t o r e d i n the IMS/VS a p p l i c a t i o n program l i b r a r y and a r e used d u r i n g b a t c h e x e c u t i o n s of the system. B a t c h programs can run e i t h e r i n the o n l i n e e x e c u t i o n i n a B a t c h Message P r o c e s s i n g Region or i n a B a t c h R e g i o n . In both cases a Database can be a c c e s s e d f o r update by o n l y one a p p l i c a t i o n program a t a t i m e . See #11.1 A p p l i c Prog f a c . R e f e r e n c e s : 3 0 ( 1 1 ) , 16(1-17) 92 L o c a l Support F a c i l i t i e s Quest i o n 14:. S e n s i t i v i t y of the DBMS t o new r e l e a s e s of the o p e r a t i n g system Assessment: IMS/VS as an e x t e n s i o n of the c a p a b i l i t i e s of the OS i s s e n s i b l e t o changes. I t i s recommended t h a t f o r proper e x e c u t i o n of IMS/VS, the system d e f i n i t i o n and system e x e c u t i o n be performed under the same O p e r a t i n g System r e l e a s e . For example, u n l e s s i t - i s a requ i r e m e n t i n the OS, a new IMS/VS system d e f i n i t i o n u s i n g the same IMS/VS r e l e a s e does not make i t n e c e s s a r y t o r e c o m p i l e user a p p l i c a t i o n programs R e f e r e n c e s : 9(4) Qu e s t i o n 17: S e n s i t i v i t y of DBMS a p p l i c a t i o n s t o r e l e a s e s of the DBMS. A b i l i t y of o l d a p p l i c a t i o n s t o use new v e r s i o n s of the DBMS and of new a p p l i c a t i o n s t o use o l d v e r s i o n s of the DBMS Assessment: A f a i r degree of c o m p a t i b i l i t y . A p p l i c a t i o n programs, i n IMS/VS v e r s i o n 1, u s i n g the Message Format S e r v i c e and i n p u t c u r s o r f i e l d may r e q u i r e a minor change. R e l e a s e s 1.4, 1.5 and 1.6 t h a t uses M u l t i p l e C o u p l i n g F e a t u r e w i l l have t o unde r t a k e c e r t a i n m o d i f i c a t i o n b e f o r e r e l e a s e 2 i s i n s t a l l e d R e f e r e n c e s : 1(2) Qu e s t i o n 36: E x i s t e n c e of t o o l s f o r programming e x p e r t s t o use i n r e p a i r i n g DBMS bugs, and i n r e c o v e r i n g the DBMS from c i r c u m s t a n c e s i n which normal backup and r e c o v e r y f a c i l i t i e s have f a i l e d Assessment: An emergency r e s t a r t i s p r o v i d e d by IMS/VS t h a t h a n d l e s the c o n d i t i o n caused by an ABEND of IMS/VS or a machine e r r o r Mechanisms: A message i s send t o the OS/VS c o n s o l e . To r e c o v e r the system l o g the OS/VS DUMP command can be used t o c r e a t e a dump d a t a s e t t h a t can be used when an emergency r e s t a r t i s begun. The system l o g i s c l o s e d o n l i n e by IMS/VS d u r i n g an emergency r e s t a r t R e f e r e n c e s : 5(3) Qu e s t i o n 69: A v a i l a b i l i t y and q u a l i t y of DBMS-maintained performance s t a t i s t i c s and r e p o r t i n g f a c i l i t i e s t h e r e o n Assessment: IMS/VS S t a t i s t i c a l A n a l y s i s U t i l i t y , F i l e S e l e c t i n g F o r m a t t i n g P r i n t Program and the Log T r a n s a c t i o n A n a l y s i s U t i l i t i y a r e the main f a c i l i t i e s t o produce r e p o r t s about performance Mechanisms: A l l of these u t i l i t i e s run w i t h the System Log da t a s e t . The System Log da t a s e t c o n t a i n s a l l i n p u t s o utput messages, a l l k i n d s of r e f e r e n c e s made t o a Data 93 Base, a l l uses of DL/I , e t c . The IMS/VS Log Tape Merge U t i l i t y i s p r o v i d e d f o r merging up t o n i n e IMS/VS i n p u t l o g t a p e s , which can be used as i n p u t t o the o t h e r u t i l i t i e s R e f e r e n c e s : 6(9) Q u e s t i o n 98 R e l a t i v e c o m p l e x i t y of p r o c e d u r e s f o r i n s t a l l i n g new v e r s i o n s of the DBMS and a d j u n c t programs Assessment: Not v e r y easy. U s u a l l y a new system g e n e r a t i o n w i l l be recommended. Some new f e a t u r e s , from r e l e a s e t o r e l e a s e do not o f f e r any d i f f i c u l t y f o r i n s t a l l a t i o n i n o l d v e r s i o n s , w h i l e o t h e r s may r e q u i r e a d d i t i o n a l m o d i f i c a t i o n s i n the O p e r a t i n g Systems. In a d d i t i o n a new r e l e a s e can d i f f e r a l o t from p r e v i o u s r e l e a s e s . For example, the Program I s o l a t i o n F e a t u r e f o r c o n c u r r e n c y s u p p o r t i n g was an o p t i o n a l f e a t u r e i n e a r l i e r r e l e a s e s . W i th the i n c r e a s e i n c o n c u r r e n c y s u p p o r t i n g and f a c i l i t i e s f o r database d i s t r i b u t i o n i t became p a r t of the DBMS package a f t e r r e l e a s e 1.5 R e f e r e n c e s : 9 Q u e s t i o n 1 4 1 : . Ease of m a i n t a i n i n g c o n f i g u r a t i o n i n f o r m a t i o n - - w h a t s t o r a g e d e v i c e s or a r e a s a r e i n use, what a p p l i c a t i o n programs use the DBMS, what user IDs t h e r e a r e , what t e r m i n a l s use the DBMS, and so on Assessment: I t i s easy e i t h e r u s i n g the master t e r m i n a l or by r u n n i n g some of the u t i l i t i e s such as SMU or the Resource Access C o n t r o l F a c i l i t y . The main c o n t r o l i s from the Master T e r m i n a l Mechanisms: The master t e r m i n a l can r e c e i v e system messages and i s a l l o w e d t o s t a r t , s t o p and r e s t a r t IMS/VS. Master t e r m i n a l can d i s p l a y the s t a t u s of the system and i t s r e s o u r c e s . I t can d i s p l a y number of programs and dat a b a s e s t h a t a re a c t i v e , number of t r a n s a c t i o n s t o be p r o c e s s e d , number of a c t i v e t e r m i n a l s , number of l o g i c a l t e r m i n a l s . The command used i s /DISPLAY w i t h s e v e r a l opt i o n s R e f e r e n c e s : 10(1),23,27 Q u e s t i o n 143: A v a i l a b i l i t y and q u a l i t y of b u i l t - i n d i a g n o s t i c f e a t u r e s — e r r o r l o g s , event t r a c e s , s e l e c t a b l e o p e r a t i o n t r a p s , e t c . Assessment: D i a g n o s t i c s f e a t u r e s a r e m a i n l y i n the way of messages and codes. I n s t a l l a t i o n s a r e f r e e t o d e f i n e c e r t a i n e r r o r r o u t i n e s t o handle some s p e c i f i c codes R e f e r e n c e s : 6 Q u e s t i o n 158: A v a i l a b i l i t y and q u a l i t y of database dump/reload f u n c t i o n s — whether p a r t i a l dumps and r e l o a d s a r e p o s s i b l e , whether dump and r e l o a d o p e r a t e s on l o g i c a l or p h y s i c a l p o r t i o n s 94 of the d a t a b a s e , whether a database can be dumped or r e l o a d e d w h i l e i t i s b e i n g used, ... Assessment: S e v e r a l o p t i o n s f o r dump r e l o a d d a t a b a s e s Mechanisms: The Image Copy U t i l i t y p e r m i t s g e t t i n g . a backup copy of a Database. I t can o p e r a t e on e i t h e r p h y s i c a l or l o g i c a l d a t a b a s e . P a r t i a l dumps are a l l o w e d t o o , and i n both c a s e s a r e OS/VS j o b s . A database can not be used w h i l e i t i s b e i n g dumped or r e l o a d e d R e f e r e n c e s : 6 Q u e s t i o n 159: How c o s t l y database dumps and r e l o a d s a r e - - i n p a r t i c u l a r , whether dumps and r e l o a d s a re p r a c t i c a l a t a l l f o r v e r y l a r g e d a t a b a s e s Assessment: Not known about c o s t . They can be p r a c t i c a l f o r p r o d u c i n g back-up c o p i e s or when a r e o r g a n i z a t i o n i s goin g t o t a k e e f f e c t Mechanisms: Dumps and r e l o a d s are s t a n d a r d OS/VS j o b s . The c o s t i s m a i n l y i n the time the database w i l l not be a v a i l a b l e . They can be p r a c t i c a l when performance of the response time f o r a p a r t i c u l a r database has degenerate t o an i n a c c e p t a b l e l e v e l . For example i n HISAM database d e l e t e d segments s t i l l occupy s t o r a g e t h a t i s t r a v e r s e d each time a t r a n s a c t i o n i s p r o c e s s e d . I f a database i s too l a r g e , p a r t i a l r e o r g a n i z a t i o n i s a v a i l a b l e . R e f e r e n c e s : 6 Q u e s t i o n 184: Ease of d i s p l a y i n g o p e r a t i o n a l s t a t u s of the DBMS ( i . e . programs r u n n i n g , t e r m i n a l s enabled) Assessment: The master t e r m i n a l p r o v i d e s f o r means t o d i s p l a y o p e r a t i o n a l s t a t u s of the system. I t p r o v i d e s f o r a way to d e t e c t programs r u n n i n g , databases a c t u a l l y i n used, l o g i c a l , and p h y s i c a l t e r m i n a l s c o n n e c t e d t o the d a t a b a s e s , e t c . See #141 A r c h i t e c t u r e Mechanisms: Master t e r m i n a l p r o v i d e s f a c i l i t i e s s i m i l a r t o the m o n i t o r f o r the O p e r a t i n g System R e f e r e n c e s : 10 95 P o r t a b i l i t y Q u e s t i o n 105: C o m p a t i b i l i t y of DBMS w i t h u s u a l data p r o c e s s i n g a p p l i c a t i o n environments Assessment: Compatible Mechanisms: Cobol and PL/1 are among the most w i d e l y used languages f o r d a t a p r o c e s s i n g Quest i o n 111: What computing environments a r e c a p a b l e of r u n n i n g the DBMS ( i . e . , how p o r t a b l e the DBMS i s ) Assessment: IMS/VS runs under the v i r t u a l s t o r a g e s o p e r a t i n g systems OS/VS1 and OS/VS2 i n systems IBM/370 models 138, 145, 1 5 5 I I , 158,16511 and 168, on the 303X and 4300 p r o c e s s o r s , and on any o t h e r c o m p a t i b l e machine. R e f e r e n c e s : 1(4),9(3) Quest i o n 151: How p o r t a b l e the DBMS da t a i s Assessment: C e r t a i n degree of p o r t a b i l i t y Mechanisms: IMS/VS, i n a d d i t i o n t o the b a s i c t y p e s of Data Bases, p r o v i d e s f o r SHSAM, SHISAM,and GSAM dat a b a s e s f o r c o n v e r t i n g from one non database system t o IMS/VS and v i c e v e r s a . They a l l o w IMS/VS a p p l i c a t i o n programs ( u s i n g OS/VS a c c e s s methods) t o pass d a t a t o non- database a p p l i c a t i o n programs and v i c e v e r s a . The d i f f e r e n c e s between SHSAM, SHISAM and GSAM i s i n the k i n d of O p e r a t i n g System a c c e s s method used, i f v a r i a b l e r e c o r d s a r e a l l o w e d , i f they can use segment e d i t / c o m p r e s s i o n f a c i l i t y , and o t h e r s . R e f e r e n c e s : 2(4) Q u e s t i o n 188: A v a i l a b i l i t y and q u a l i t y of t o o l s t o a i d i n m i g r a t i n g a p p l i c a t i o n programs and da t a t o or from o t h e r DBMS environments Assessment: A p p l i c a t i o n programs depend on t h e i r a s s o c i a t e PSB making d i f f i c u l t t o m i g r a t e them t o o t h e r DBMS i n s t a l l a t i o n s . S i m i l a r l y an a p p l i c a t i o n programs coming from o t h e r i n s t a l l a t i o n needs a PSB b e f o r e i t can be ex e c u t e d . IMS/VS p r o v i d e s , i n a d d i t i o n t o the f o u r b a s i c mathods of a c c e s s s t o r a g e , a Simple HSAM, Simple HISAM and G e n e r a l i z e d S e q u e n t i a l Access Method t o a l l o w non-IMS/VS a p p l i c a t i o n programs t o a c c e s s d a t a s e t s c o n t a i n i n g database d a t a . These same f a c i l i t i e s p r o v i d e f o r IMS/VS a p p l i c a t i o n programs f o r a c c e s s i n g non IMS/VS d a t a . R e f e r e n c e s : 10 96 R e l i a b i l i t y Quest i o n 66.1: Degree t o which the DBMS gu a r a n t e e s t h a t no t r a n s a c t i o n w i l l l e a v e the database i n an i n c o n s i s t e n t s t a t e even i f system c r a s h e s , s t o r a g e d e v i c e f a i l u r e s or o t h e r e n v i r o n m e n t a l e r r o r s o c c u r Assessment: A l l t r a n s a c t i o n s , messages, e t c a r e r e c o r d e d i n the system t r a n s a c t i o n l o g . I f a RESTART command i s i s s u e d a l l suspended messages a re taken back i n t o the r e s p e c t i v e queues. See #19 ON BACKUP ... R e f e r e n c e s : 5(1) Qu e s t i o n 107: Degree t o which e r r o r s i n the o p e r a t i n g o p e r a t i n g system environment tend t o make the DBMS u n a v a i l a b l e ( f a u l t i n t o l e r a n c e ) Assessment: I f OS/VS f a i l s the DBMS tends t o be u n a v a i l a b l e Mechanisms: I f OS/VS f a i l s v i r t u a l s t o r a g e i s c o p i e d t o a dump d a t a s e t , t h a t l a t e r i s used t o s t a r t IMS/VS. IBM o f f e r s a power warning f e a t u r e t h a t i s under c o n t r o l of IMS/VS, t h a t works w i t h a n o n i n t e r r u m p i b l e power s u p p l y . T h i s equipment i s a v a i l a b l e o n l y f o r systems 370 models 158 or 168.See 66.1 backup t o o R e f e r e n c e s : 5(3) Qu e s t i o n 108: Degree t o which a p p l i c a t i o n p r o g r a e r r o r s t e n d t o make the DBMS u n a v a i l a b l e — p a r t i c u l a r l y , whether one program's e r r o r s t e n d t o make the DBMS or the database u n a v a i l a b l e t o o t h e r , i n n o c e n t programs, e.g. the case i n which DBMS common memory i s i n a p p l i c a t i o n program a d d r e s s space Assessment: No Mechanisms: See #65 Qu e s t i o n 128: A v a i l a b i l i t y and q u a l i t y of f e a t u r e s f o r a u t o m a t i c a l l y d e t e c t i n g damaged databases Assessment: Damaged Databases can not be d e t e c t e d i n any au t o m a t i c way. Programs t r y i n g t o a c c e s s a damaged database w i l l produce and ABEND message r e p o r t e d t o the master t e r m i n a l . The master t e r m i n a l , t h r o u g h the use of the command /DISPLAY DATABASE <options> can f i n d the s t a t u s or d e t e c t i f i t i s damaged and i n i t i a l i z e r e c o v e r y o p t i o n s R e f e r e n c e s : 22 Qu e s t i o n 129: Whether e r r o r h a n d l i n g tends t o be l o c a l i z e d , or whether e r r o r s tend t o make the DBMS g l o b a l l y u n a v a i l a b l e Assessment: E r r o r s tend t o be l o c a l i z e d Mechanisms: I t uses c h e c k p o i n t s i n s e v e r a l s t a g e s of the o p e r a t i o n and send messages about e r r o r c o n d i t i o n s . The 97 master t e r m i n a l i s a b l e t o t e r m i n a t e the s e s s i o n of a t e r m i n a l where the e r r o r was o r i g i n a t e d R e f e r e n c e s : 8(4) Q u e s t i o n 161: Degree t o which the d a t a i s p r o t e c t e d from p h y s i c a l damage, e.g. a d i s k head c r a s h Assessment: A l l t r a n s a c t i o n s a r e r e c o r d e d i n the System Log t h a t i s used f o r r e c o v e r y purposes Mechanisms: The l o g tape must be c l o s e d b e f o r e u s i n g i t w i t h the r e c o v e r y u t i l i t i e s . I f i t i s not c l o s e d i t must be used w i t h the dump d a t a s e t s when IMS/VS i s emergency r e s t a r t e d . I f the system l o g can not be r e c o v e r y i n i t s t o t a l i t y t h e r e e x i s t some r e c o v e r y u t i l i t i e s p r o v i d e d by IMS/VS t o such e f f e c t . The r o u t i n e s a r e used t o check s t a t u s of the l o g tape and d e t e c t p o s s i b l e e r r o r s . R e f e r e n c e s : 5(1) Q u e s t i o n 162: Degree t o which the d a t a i s p r o t e c t e d from e f f e c t s of hardware or s o f t w a r e f a i l u r e s d u r i n g u p d a t i n g Assessment: When a power f a i l u r e o c c u r s the c o n t e n t s of r e a l s t o r a g e i s w r i t t e n t o a d a t a s e t d e s i g n a t e d s p e c i f i c a l l y f o r t h i s purpose. When power i s s u p p l i e d and OS/VS i s a c t i v e the Log Tape Recovery U t i l i t y i s run f o r a l l o n l i n e Data Bases t h a t were b e i n g updated when system f a i l e d . NOTE: A c c o r d i n g t o O p e r a t o r ' s R e f e r e n c e Manual some i n p u t t r a n s a c t i o n s may be l o s t and some d u p l i c a t e output messages may be ge n e r a t e d a f t e r r u n n i n g t h i s p r o c e d u r e . IMS/VS p r o v i d e s w i t h a Power Warning F e a t u r e , t h a t i s o p t i o n a l . R e f e r e n c e s : 5(3) 98 S e c u r i t y Q u e s t i o n 22: " G r a n u l a r i t y " of a c c e s s a u t h o r i z a t i o n s y s t e m — w h e t h e r i n d i v i d u a l a c c e s s a u t h o r i z a t i o n s p e c i f i c a t i o n s can be r e s t r i c t e d t o s u b s e t s of the d a t a , and, i f so, what k i n d s and s i z e s of s u b s e t s can e x i s t Assessment: Down t o the f i e l d l e v e l Mechanisms: The PCB, u s i n g the SENSEG macro statement can be used by the DBA t o d e f i n e which segments the user program can a c c e s s . W i t h i n a segment the SENFLD macro statement c o n t r o l s f i e l d a c c e s s . The PCB's r e q u i r e d by a program c o n s t i t u t e the PSB f o r t h a t program and they a re l o a d e d f i r s t . R e f e r e n c e s : 6(2) Q u e s t i o n 24: When a c c e s s a u t h o r i z a t i o n can and cannot be s p e c i f i e d — d u r i n g database d e f i n i t i o n , when the da t a i s e n t e r e d , or any time Assessment: Access a u t h o r i z a t i o n a re s p e c i f i e d as p a r t of Program S p e c i f i c a t i o n B l o c k g e n e r a t i o n which can be run d u r i n g Data Base G e n e r a t i o n or a f t e r w a r d s . Mechanisms: A program S p e c i f i c a t i o n B l o c k (PSB) i s c r e a t e d t o d e f i n e the d a t a s t o r a g e s t r u c t u r e r e q u i r e d by an a p p l i c a t i o n program. A PSB c o n t a i n s one or more PCB (Program Communication B l o c k s ) , one f o r each h i e r a r c h i c a l d a t a s t r u c t u r e the program i n t e n d s t o use. Each PCB d e f i n e s the h i e r a r c h i c a l ( s u b ) s t r u c t u r e the program sees from the p h y s i c a l or l o g i c a l d a t a b a s e . I t s p e c i f i e s f o r each segment the k i n d s of a c c e s s a l l o w e d by the program, t h a t i s , read o n l y , update, i n s e r t and/or d e l e t e . The PSB, i n a s i m i l a r way t o the DBD,is c r e a t e d by the r u n n i n g of the macro u t i l i t y PSBGEN and the o b j e c t code i s s t o r e d i n a PSB l i b r a r y . T h i s PSB l i b r a r y i s a c c e s s e d by IMS/VS a t l o a d time and b e f o r e the program i s g i v e n c o n t r o l . See # 27 t h i s s e c t i o n R e f e r e n c e s : 10(5),16(1) Q u e s t i o n 25 Whether the a u t h o r i t y t o c o n t r o l a c c e s s can be d e l e g a t e d Assessment: C o n t r o l a c c e s s can not be d e l e g a t e d Mechanisms: Each program has i t s own Program S p e c i f i c a t i o n B l o c k d e f i n e d by the DBA and r e s i d i n g i n the PSB l i b r a r y . R e f e r e n c e s : 2(6.5) Q u e s t i o n 26: Impact of s e c u r i t y system on DBMS performance Assessment: S e c u r i t y f e a t u r e s of IMS/VS a r e b u i l t - i n and t h e r e i s no measurement of t h e i r impact on system performance Mechanisms: IMS/VS da t a s e c u r i t y i s a c h i e v e d u s i n g d e f i n i t i o n of l o g i c a l d a t abases ( u s e r views) and g e n e r a t i o n of the 99 PCB's f o r a program, which i s a b a s i c f e a t u r e of IMS/VS. A l l programs have t o have a PSB which i s l o a d e d b e f o r e the program t a k e s c o n t r o l . Hence t h i s type of s e c u r i t y can not be c o n s i d e r e d t o have a s e p a r a t e overhead. IMS/VS t e r m i n a l and t r a n s a c t i o n type s e c u r i t y i s r e l a t i v e s i m p l e and i s invoked i n f r e q u e n t l y compared t o the normal f r e q u e n c i e s of d a t a r e f e r e n c e . Hence, no s e c u r i t y f e a t u r e c o u l d be s a i d t o a f f e c t performance s i g n i f i c a n t l y R e f e r e n c e s : 5(4.2),10(6.3) Q u e s t i o n 27: Ease of use of s e c u r i t y system Assessment: Data s e c u r i t y i s easy t o un d e r s t a n d but i n c o n v e n i e n t l y s t a t i c . T e r m i n a l and t r a n s a c t i o n type s e c u r i t y i s easy t o u n d e r s t a n d and somehow more dynamic Mechanisms: Data s e c u r i t y i s s e p e c i f i e d i n l o g i c a l database o p t i o n s g i v e n as p a r t of the SENSEG macro statement of the PCB d e f i n i t i o n s . T h e r e f o r e knowing how t o d e f i n e l o g i c a l d atabases i s s u f f i c i e n t t o d e f i n e d a t a s e c u r i t y . However, changing a c c e s s a u t h o r i z a t i o n s t o an e x i s t i n g program may r e q u i r e the r e g e n e r a t i o n of i t s PSB, which i s i n c o n v e n i e n t . T e r m i n a l and t r a n s a c t i o n - t y p e s e c u r i t y i s s p e c i f i e d v i a t h e SMU ( S e c u r i t y Maintenance U t i l i t y ) which can be run at any t i m e . The master t e r m i n a l p r o v i d e s f o r a dynamic c o n t r o l of some of the c o n f i g u r a t i o n d e t a i l s s e t up by SMU R e f e r e n c e s : 2(6.5) Q u e s t i o n 29: How l a t e a c c e s s a u t h o r i z a t i o n s a re bound t o an a p p l i c a t i o n program--at c o m p i l e t i m e , l o a d t i m e , or when the d a t a a c c e s s i s made Assessment: At l o a d time Mechanisms: When a program i s s c h e d u l e d f o r e x e c u t i o n i t s p e c i f i e s i t s PSB by means of a JCL sta t e m e n t . IMS/VS f e t c h e s and l o a d s i n t o s t o r a g e the DBD's and the PCB's r e q u i r e d from t h e i r r e s p e c t i v e l i b r a r i e s . IMS/VS checks f o r s e c u r i t y o p t i o n s and determine s e c u r i t y o p t i o n s f o r the program. I t , then l o a d s the a p p l i c a t i o n program and g i v e s i t c o n t r o l , p a s s i n g the PCB's a d d r e s s e s as parameters R e f e r e n c e s : 2(4) Q u e s t i o n 30.1: How complex an a c c e s s c o n s t r a i n t may be--what c r i t e r i a ( d a t a o b j e c t name, d a t a o b j e c t v a l u e , u s e r - s u p p l i e d d a t a , user ID, t e r m i n a l ID, time of day, e t c . ) a r e a v a i l a b l e and what r e l a t i o n s h i p s between them can be d e f i n e d Assessment: C o n s t r a i n t s t h a t d e f i n e a c c e s s t o programs i n c l u d e t e r m i n a l ID, user ID, and d a t a o b j e c t name. The c o n s t r a i n t s , when combined, can be q u i t e complex. For example, a s p e c i f i e d user may o n l y be a l l o w e d t o use a p a r t i c u l a r t e r m i n a l t o p r o c e s s c e r t a i n t r a n s a c t i o n s u s i n g a few a l l o w e d commands. C r i t e r i a such as time of day, 100 d a t a o b j e c t v a l u e , and u s e r - s u p p l i e d d a t a a re not r e a d i l y a v a i l a b l e . C o n s t r a i n t s t h a t d e f i n e program a c c e s s t o the da t a a r e not v e r y complex. Access a t t h i s l e v e l i s c o n t r o l l e d by user views d e f i n e d by the DBA. The views can be d e f i n e d down t o the f i e l d l e v e l •Mechanisms: Access c o n t r o l s on programs a r e s e t up by e x e c u t i n g S e c u r i t y M a i n t a i n e n c e U t i l i t y ( S M U ) a f t e r system d e f i n i t i o n . The master t e r m i n a l o p e r a t o r ( M T O ) , however, can modify a l l s e c u r i t y p r o f i l e s d u r i n g normal o p e r a t i o n s , or d u r i n g normal r e s t a r t , s u b j e c t t o normal l i m i t a t i o n s imposed by system d e f i n i t i o n . A c c ess c o n t r o l s on the program-data i n t e r f a c e a re d e f i n e d , u s i n g SENSEG and SENSFLD statements i n the PCB's a program w i l l be a u t h o r i z e d t o a c c e s s . R e f e r e n c e s : 3 ( 1 3 ) , 4 ( 6 ) , 10(11) Q u e s t i o n 31: A v a i l a b i l i t y and q u a l i t y of s e c u r i t y m o n i t o r i n g t o o l s , e.g. a u d i t t r a i l Assessment: The l o g g i n g f a c i l i t y p r o v i d e s a good a u d i t t r a i l f o r the m o n i t o r i n g of s e c u r i t y . Mechanisms: A l l messages e n t e r i n g and l e a v i n g the system, and a l l changes t o the database a re r e c o r d e d on l o g t a p e s . The l o g tape r e f l e c t s the s t a t e of the system a t t h a t p o i n t i n t i m e . The l o g tape i s a l s o used t o r e s t a r t the system a f t e r i t was s t o p e d f o r any reason R e f e r e n c e s : 23(1 . 2) Q u e s t i o n 32: How s e c u r i t y e x c e p t i o n s a re handl e d Assessment: S e c u r i t y v i o l a t i o n s a re r e c o r d e d on the IMS/VS system l o g t a p e . T h i s p r o v i d e s an a u d i t t r a i l . An e r r o r message i s sent t o the t e r m i n a l e n t e r i n g the message. The master t e r m i n a l i s a l s o n o t i f i e d when a t h r e s h o l d e r r o r l i m i t i s reached. Mechanisms: The t h r e s h o l d l i m i t can be s e t by s p e c i f y i n g the number of v i o l a t i o n s b e f o r e n o t i f i c a t i o n . ( i . e . 1 t o 3 i n v a l i d e n t r i e s ) R e f e r e n c e s : 10(6) Q u e s t i o n 34 How secure the s e c u r i t y f u n c t i o n s a re Assessment: The s e c u r i t y f u n c t i o n s a re q u i t e s e c u r e . The c r i t i c a l c o n t r o l p o i n t t o the system i s the master t e r m i n a l operator(MTO), because the MTO can modify a l l s e c u r i t y p r o f i l e s d u r i n g normal o p e r a t i o n s . The MTO can be c o n t r o l l e d u s i n g LTERM s e c u r i t y , s i g n o n v e r i f i c a t i o n , and by e n f o r c i n g s e c u r i t y o p t i o n s . T h i s assessment r e f l e c t s o n l y the s e c u r i t y of IMS/VS. I t does not r e f l e c t the s e c u r i t y of the o p e r a t i n g system on which i t i s dependent upon. Mechanisms: LTERM and s i g n o n v e r i f i c a t i o n s e c u r i t y f e a t u r e s a r e p a r t of SMU. The s i g n o n v e r i f i c a t i o n w i l l i d e n t i f y the MTO w h i l e the LTERM s e c u r i t y a l l o w s you t o s p e c i f y 101 \ the commands the MTO i s a l l o w e d t o use. At c o l d or warm s t a r t t i m e , the MTO can c o n t r o l many s e c u r i t y f e a t u r e s : s i g n o n v e r i f i c a t i o n s e c u r i t y , t r a n s a c t i o n a u t h o r i z a t i o n , t e r m i n a l s e c u r i t y , t r a n s a c t i o n command s e c u r i t y , and password s e c u r i t y . T h i s can be p r o h i b i t e d u s i n g SECURITY macro keywords. R e f e r e n c e s : 10(6) Q u e s t i o n 182: A b i l i t y t o d e f i n e u s e r - w r i t t e n s e c u r i t y - c o n t r o l p r o c e d u r e s , e.g. a c c e s s - c h e c k i n g r o u t i n e s , s p e c i a l l o g g i n g f u n c t i o n s , e t c . Assessment: Yes, the user i s a b l e t o w r i t e h i s own t r a n s a c t i o n a c c e s s i n g m a i n t a i n e n c e u t i l i t i e s , and a l s o s e c u r i t y f u n c t i o n s a t the program-data i n t e r f a c e . Mechanisms: T r a n s a c t i o n a c c e s s c o n t r o l i n v o l v e s a t a b l e which can be m a i n t a i n e d by normal a p p l i c a t i o n programs. Program-data s e c u r i t y f u n c t i o n s can be implemented by s u b r o u t i n e s c a l l e d by the segment e d i t / c o m p r e s s i o n e x i t . R e f e r e n c e s : 10(6) Q u e s t i o n 197: Whether a c c e s s c o n t r o l f a c i l i t i e s make i t p o s s i b l e t o e x c l u d e a c c e s s o r s as e a s i l y as t o i n c l u d e t h e m — e . g . whether a c c e s s can be g r a n t e d t o a l l employees i n department X EXCEPT employee A Assessment: None a v a i l a b l e 1 02 Soft w a r e Q u a l i t y Quest i o n 113: Q u a l i t y of the DBMS i n t e r f a c e t o the o p e r a t i n g system Assessment: OS/VS has t o under t a k e c e r t a i n m o d i f i c a t i o n s b e f o r e IMS/VS can be e x e c u t e d . C e r t a i n s t a n d a r d OS/VS . system g e n e r a t i o n o p t i o n s and some non s t a n d a r d o p t i o n s are r e q u i r e d b e f o r e IMS/VS can be e x e c u t e d R e f e r e n c e s : 9(4) Q u e s t i o n 131: Whether the DBMS i s w r i t t e n i n a modern programming language Assessment: No, IMS/VS i s w r i t t e n i n Assembler Language R e f e r e n c e s : 1(3) Q u e s t i o n 132: Q u a l i t y of the DBMS o p e r a t i n g system i n t e r f a c e — i n p a r t i c u l a r , degree t o which o p e r a t i n g system f u n c t i o n s are i n v o k e d from one (or a s m a l l number) of p l a c e s i n the DBMS code, and the degree t o which the r e p e r t o i r e of o p e r a t i n g system s e r v i c e s used i s w e l l - d e f i n e d Assessment: These s e r v i c e s a r e v e r y c o m p l i c a t e d and d i f f i c u l t t o u n d e r s t a n d . At times i s almost i m p o s s i b l e t o s e p a r a t e s e r v i c e of the OS and IMS/VS i t s e l f Mechanisms: IMS/VS uses the OS/VS t o p e r f o r m such a c t i v i t i e s as I n p u t / O u t p u t , s t o r a g e management and t a s k management. R e f e r e n c e s : 8(1) 103 APPENDIX 2. UNANSWERED EVALUATION CRITERIA A p p l i c a t i o n Programming F a c i l i t i e s 192 A v a i l a b i l i t y and q u a l i t y of c o m p i l e r s or p r e c o m p i l e r s f o r languages t h a t i n c l u d e d a t a m a n i p u l a t i o n f e a t u r e s , and degree t o which those c o m p i l e r s have knowledge of the d a t a def i n i t i o n A r c h i t e c t u r e , Computing Environment, Parameter L i m i t s , and  M u l t i t h r e a d i n g 10 Memory-management s e r v i c e s r e q u i r e d from the o p e r a t i n g system (e.g. dynamic memory a l l o c a t i o n , s h a r ed memory among m u l t i p l e t a s k s , e t c . ) Data Model 1.16 Whether r e p e a t i n g f i e l d s ( i . e ; , f i e l d s which a r e a r r a y s ) a r e a l l o w e d Data S t o r a g e 195 A v a i l a b i l i t y , q u a l i t y , and e f f i c i e n c y of f e a t u r e s f o r m i g r a t i n g l e s s f r e q u e n t l y used d a t a t o cheaper, slo w e r s t o r a g e . A l s o , degree of g r a n u l a r i t y and degree of t r a n s p a r e n c y of such m i g r a t i o n s , and degree t o which they a r e performed a u t o m a t i c a l l y 198 Degree t o which d a t a can be p l a c e d i n p h y s i c a l s t o r a g e so as to t a k e advantage of c l u s t e r i n g of d a t a v a l u e s f o r i m p r o v i n g speed of a c c e s s D i s t r i b u t e d Database F a c i l i t i e s 1 77 Communications bandwidth r e q u i r e d t o run m u l t i p l e , i n t e r c o n n e c t e d i n v o c a t i o n s of the DBMS i n s e p a r a t e computer systems, as a f u n c t i o n of t r a n s a c t i o n r a t e and database s i z e Ef f i c i e n c y 3 D i f f e r e n c e i n p r o c e s s i n g c o s t s between i n q u i r y and update t r a n s a c t i o n s 5 Amount of d y n a m i c a l l y - a c q u i r e d p r o c e s s o r memory r e q u i r e d as a f u n c t i o n of DBMS s e r v i c e demand 6 Degree t o which the DBMS imposes p a g i n g l o a d on a v i r t u a l -memory environment as a f u n c t i o n of s e r v i c e demand (e.g. working s e t s i z e ) Human I n t e r f a c e s 104 1 45 Ge n e r a l amount of t r a i n i n g r e q u i r e d t o use DBMS L o c a l Support F a c i l i t i e s 97 Whether the source code f o r the DBMS i s a v a i l a b l e t o customers P o r t a b i l i t y 189 A v a i l a b i l i t y and q u a l i t y of f e a t u r e s t o a l l o w a c c e s s i n g o t h e r database management systems' d a t a R e l i a b i l i t y 109 A v a i l a b i l i t y and q u a l i t y of b u i l t - i n f e a t u r e s t o d e t e c t and re c o v e r from i n t e r n a l DBMS s o f t w a r e e r r o r s S o f t w a r e Q u a l i t y 106 Bug - f r e e n e s s of the DBMS s o f t w a r e 115 Amount of DBMS and a d j u n c t programs code 1 33 Degree of s t a n d a r d i z a t i o n w i t h the DBMS—whether the code i s w r i t t e n a c c o r d i n g t o e x p l i c i t c o n v e n t i o n s , degree t o which i n t e r n a l i n t e r f a c e s a r e d e f i n e d , e t c . 1 34 Degree t o which the DBMS and a d j u n c t programs a r e composed of c l e a n l y s e p a r a t e d modules and/or a r c h i t e c t u r a l l a y e r s , w i t h each m o d u l e / l a y e r h a v i n g w e l l - d e f i n e d f u n c t i o n s and e x t e r n a l i n t e r f a c e s ( m o d u l a r i t y ) 1 35 Given a r e l a t i v e l y modular DBMS, whether the c h o i c e s of which modules t h e r e are and what each module does a r e r e a s o n a b l e 1 37 Q u a l i t y of the DBMS's i n t e r n a l c o n t r o l b l o c k s t r u c t u r e s 138 Degree t o which the DBMS's d e s i g n tends t o a l l o w easy growth of usage parameters and l i m i t s ( e.g. number and maximum number of d a t a b a s e s , number and maximum number of u s e r s , ...) as opposed t o the degree t o which the DBMS d e s i g n tends t o l i m i t e x p a n s i o n 1 39 Whether the DBMS and a d j u n c t programs' code modules have t r a c t a b l y s m a l l s i z e s 1 44 Q u a l i t y of the DBMS and a d j u n c t programs c o d e — t y p e s of c o d i n g s t r u c t u r e s , use of i d e n t i f i e r s , q u a n t i t y and q u a l i t y of source comments, e t c . 105 APPENDIX 3: GLOSSARY OF TERMS S u b j e c t C a t e g o r i e s : M u l t i t h r e a d i n g . the r u n n i n g of more than one a p p l i c a t i o n p r o c e s s a t the same time Parameter l i m i t s . TT) r e s t r i c t i o n s on c o m p l e x i t y of d a t a d e f i n i t i o n or amount of da t a i n database 2.) o t h e r o p e r a t i n g parameters such as maximum number of c o n c u r r e n t u s e r s , e t c . A r c h i t e c t u r e . What i s the DBMS d e s i g n l i k e and how good i s i t ? S o f t w a r e q u a l i t y . q u a l i t y of code, u s e f u l n e s s of e r r o r d i a g n o s t i c s , e t c . Communications f a c i l i t i e s . telecommunications., n e t w o r k i n g , t e r m i n a l s upport Computing environment, o p e r a t i n g system and hardware Terms: Data d e f i n i t i o n d a t a , d a t a t h a t the DBMS needs t o run Data A d m i n i s t r a t i o n d a t a . d a t a t h a t the DBA needs to do h i s job Data d e s c r i p t i o n d a t a , union of the above two T r a n s a c t i o n . A group of a c t i o n s by the same user which i s c o n s i s t e n c y p r e s e r v i n g . That i s , a t r a n s a c t i o n when • e x e c u t e d a l o n e t r a n s f o r m s a c o n s i s t e n t database i n t o a new c o n s i s t e n t s t a t e (assuming no hardware or s o f t w a r e e r r o r s ) . Note t h a t the database may be t e m p o r a r i l y i n c o n s i s t e n t d u r i n g e x e c u t i o n of a t r a n s a c t i o n . Concurrency s u p p o r t i n g . A DBMS i s c o n c u r r e n c y s u p p o r t i n g i f i t a l l o w s s i m u l t a n e o u s l y e x e c u t i n g t r a n s a c t i o n s t o behave as i f they a re b e i n g e x e c u t e d one a t a t i m e . A t o m i c . i n d i v i s i b l e Ta) a p p a r e n t l y i n d i v i s i b l e - behaves as one (b) a c t u a l l y i n d i v i s i b l e - i s one. For example, an atomic t r a n s a c t i o n behaves as i f i t i s one a c t i o n and t h e r e f o r e , i s a p p a r e n t l y i n d i v i s i b l e . An atomic a c t i o n , on the o t h e r hand, i s a c t u a l l y i n d i v i s i b l e . M u l t i p r o c e s s i n g . iT) w i t h i n one s e s s i o n a b i l i t y t o have g r e a t e r than one s i m u l t a n e o u s l y e x e c u t i n g p r o c e s s owned by the same s e s s i o n . 2.) w i t h i n one o p e r a t i n g system a b i l i t y t o have g r e a t e r than one s i m u l t a n e o u s l y e x e c u t i n g p r o c e s s , whether or not owned by the same u s e r . 106 REFERENCES 1. IMS/VS GENERAL INFORMATION MANUAL (GIM), GH20-1260 IBM C o r p o r a t i o n 1980 Sept 2. IMS/VS DATA BASE ADMINISTRATION GUIDE (DBAG), SH20-9025 IBM C o r p o r a t i o n 1981 March 3. IMS/VS APPLICATION PROGRAMMING: DESIGN AND CODING (APDC), SH20-9026 IBM C o r p o r a t i o n 1981 March 4. IMS/VS SYSTEM PROGRAMMING REFERENCE MANUAL (SPRM),SH20-9027 IBM C o r p o r a t i o n J u l y 1980 5. IMS/VS OPERATORS REFERENCE MANUAL (OPRM), SH20-9028.IBM C o r p o r a t i o n 1980 J u l y 6. IMS/VS UTILITIES REFERENCE MANUAL (UTRM), SH20-9029 IBM C o r p o r a t i o n 1980 J u l y 7. MESSAGE FORMAT SERVICE USER'S GUIDE (MFS), SH20-9053 IBM C o r p o r a t i o n 1981 March 8. IMS/VS PROGRAMMING GUIDE FOR REMOTE SNA SYSTEMS (SNAP), SH20-9054 IBM C o r p o r a t i o n 1980 J u l y 9. IMS/VS INSTALLATION GUIDE ( I G ) , SH20-9081 IBM C o r p o r a t i o n 1981 March 10. IMS/VS SYSTEM ADMINISTRATION GUIDE (SAG), SH20-9078 IBM C o r p o r a t i o n 1981 March 11. IMS/VS FAST PATH GENERAL INFORMATION MANUAL ( F P G I ) , GH20-9069 IBM C o r p o r a t i o n 1978 A p r i l 12. IMS/VS MASTER INDEX AND GLOSSARY (MIG), SH20-9085 IBM C o r p o r a t i o n (March 1981) 1 07 13. IMS/VS MESSAGES AND CODES - REFERENCE MANUAL, SH20-9030 IBM C o r p o r a t i o n 1981 March 14. IMS/VS APLICATION DEVELOPMENT FACILITY - GENERAL I n f o r m a t i o n , GB21-9326 IBM C o p r p o r a t i o n 1980 J u l y 15. IMS/VS APLICATION DEVELOPMENT FACILITY - SH20-9031 IBM C o p r p o r a t i o n 1981 A p r i l 16. IMS/VS PRIMER, S320-5767 IBM C o r p o r a t i o n 1977 Ja n u a r y 17. IMS/VS PRIMER SAMPLE LISTING, SH20-9149 IBM C o r p o r a t i o n 1978 September 18. IMS/VS DATA BASE RECOVERY CONTROL FEATURE: G e n e r a l I n f o r m a t i o n GH35-0010 IBM C o r p o r a t i o n 1981 A p r i l 19. IMS/VS DATA BASE RECOVERY CONTROL FEATURE: R e f e r e n c e and O p e r a t i o n s Guide, SH35-0027 IBM C o r p o r a t i o n 1981 A p r i l 20. IMS/VS ADVANCED FUNCTIONS FOR COMMUNICATIONS, SH20-9054 IBM C o r p o r a t i o n 1977 J u l y 21. IMS/VS PRIMER REMOTE TERMINAL OPERATOR'S GUIDE, SH20-9148 IBM C o r p o r a t i o n 1978 October 22. IMS/VS PRIMER MASTER TERMINAL OPERATOR'S GUIDE - VTAM, SH20-9147 IBM C o r p o r a t i o n 1978 September 23. IMS/VS PRIMER MASTER TERMINAL OPERATOR'S GUIDE - BTAM, SH20-9146 IBM C o r p o r a t i o n 1978 September 24. IMS/VS PROGRAM PRODUCT - SPECIFICATIONS, 5740-XX2 IBM Corp o r a 25. OS/VS DB/DC DATA DICTIONARY - APPLICATION GUIDE - SH20-9190 IBM C o r p o r a t i o n 1980 Sept 108 26. OS/VS DB/DC DATA DICTIONARY - TERMINAL USER'S GUIDE AND Command R e f e r e n c e , SH20-9189 IBM C o r p o r a t i o n 1980 Sept 27. OS/VS DB/DC DATA DICTIONARY - GENERAL INFORMATION MANUAL GH20-9104 IBM C o r p o r a t i o n 1978 Oct 28. OS/VS DB/DC DATA DICTIONARY - INSTALLATION GUIDE, SH20-9191 IBM C o r p o r a t i o n 1980 Sept 29. AN INTRODUCTION TO DATABASE SYSTEMS, SECOND EDITION C.J Date Addison Wesley 1977 30. INFORMATION MANAGEMENT SYSTEM IBM Systems J o u r n a l Volume 16, number 2, 1977 31. INTERACTIVE QUERY FACILITY(IQF) FOR IMS/360, H20-1223, INTRODUCTION TO IQF LANGUAGE GUIDE, H20-1222 IBM C o r p o r a t i o n 32. AN INTRODUCTION TO DATABASE SYSTEMS, SECOND EDITION C.J Date Ad d i s o n Wesley 1977 32. INFORMATION MANAGEMENT SYSTEM IBM Systems J o u r n a l Volume 16, number 2, 1977 33. INTERACTIVE QUERY FACILITY(IQF) FOR IMS/360, H20-1223, INTRODUCTION TO IQF LANGUAGE GUIDE, H20-1222 IBM C o r p o r a t i o n 1974 

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