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UBC Theses and Dissertations
Making predictions directly from past experiences Craddock, A. Julian
Abstract
This thesis considers the problem of making predictions about new experiences based upon past experiences. The problem is of interest to artificial intelligence because past experiences are a kind of domain knowledge that is readily available to com- putational agents, and are at least one form of knowledge that humans use to make predictions. Instead of considering the problem in terms of first inducing a domain model from a set of past experiences, and then using some form of deduction to make predictions, this thesis develops a new technique called the reference class approach (RCA) that directly infers estimates of conditional probabilities from a knowledge base of past experiences. The resulting estimates can be readily used in a number of contexts such as non-monotonic reasoning, the characterisation of probability distribution functions, prediction and classification. Given a knowledge base (KB) of descriptions of past experiences, a description of a new experience, and a proposition representing a query about the new experience, the RCA estimates the conditional probability of the proposition being true of the new experience. The RCA starts by identifying a subset of the KB called the reference class that contains all those past experiences in the KB whose descriptions cover everything that is known about the new experience in addition to providing a truth value for the proposition. If there are no directly applicable past experiences, i.e., the reference class is empty, then the description of the new experience is modified until a non-empty ref- erence class can be found. This thesis investigates two new approaches to modifying the description, namely syntactic generalisation and chaining. Previous research has proposed that logical implication can be used to semantically generalise an empty reference class to any non-empty reference class. This thesis shows that semantic generalisation does not work in the context of making predictions from a KB of past experiences. This thesis argues that we should syntactically generalise the descrip- tion of the new experience. Chaining is a novel extension of syntactic generalisation that allows us to systematically increase what we know about a new experience by elaborating its description while generalising. Once a non-empty reference class has been identified the RCA estimates the conditional probability of the proposition being true by measuring the frequency with which the proposition is true in the reference class. The RCA is an inductive technique in that it estimates probabilities directly from past experiences. One useful test of an inductive technique is to test whether or not it can be used to make accurate predictions from past experiences. This thesis argues that in order to implement the RCA we need a notion of irrelevance to pick the most appropriate generalised or chained reference class. This thesis shows that even with very simple notions of irrelevance, the RCA’s estimates can be used to make predictions whose accuracy compares favourably with state of the art machine learning techniques on standard test data from the machine learning community.
Item Metadata
Title |
Making predictions directly from past experiences
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
1993
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Description |
This thesis considers the problem of making predictions about new experiences based
upon past experiences. The problem is of interest to artificial intelligence because
past experiences are a kind of domain knowledge that is readily available to com-
putational agents, and are at least one form of knowledge that humans use to make
predictions.
Instead of considering the problem in terms of first inducing a domain model
from a set of past experiences, and then using some form of deduction to make
predictions, this thesis develops a new technique called the reference class approach
(RCA) that directly infers estimates of conditional probabilities from a knowledge
base of past experiences. The resulting estimates can be readily used in a number
of contexts such as non-monotonic reasoning, the characterisation of probability
distribution functions, prediction and classification.
Given a knowledge base (KB) of descriptions of past experiences, a description of
a new experience, and a proposition representing a query about the new experience,
the RCA estimates the conditional probability of the proposition being true of the
new experience. The RCA starts by identifying a subset of the KB called the
reference class that contains all those past experiences in the KB whose descriptions
cover everything that is known about the new experience in addition to providing a
truth value for the proposition.
If there are no directly applicable past experiences, i.e., the reference class is
empty, then the description of the new experience is modified until a non-empty ref-
erence class can be found. This thesis investigates two new approaches to modifying
the description, namely syntactic generalisation and chaining. Previous research has
proposed that logical implication can be used to semantically generalise an empty reference class to any non-empty reference class. This thesis shows that semantic
generalisation does not work in the context of making predictions from a KB of past
experiences. This thesis argues that we should syntactically generalise the descrip-
tion of the new experience. Chaining is a novel extension of syntactic generalisation
that allows us to systematically increase what we know about a new experience by
elaborating its description while generalising. Once a non-empty reference class has
been identified the RCA estimates the conditional probability of the proposition
being true by measuring the frequency with which the proposition is true in the
reference class.
The RCA is an inductive technique in that it estimates probabilities directly
from past experiences. One useful test of an inductive technique is to test whether
or not it can be used to make accurate predictions from past experiences. This thesis
argues that in order to implement the RCA we need a notion of irrelevance to pick
the most appropriate generalised or chained reference class. This thesis shows that
even with very simple notions of irrelevance, the RCA’s estimates can be used to
make predictions whose accuracy compares favourably with state of the art machine
learning techniques on standard test data from the machine learning community.
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Extent |
3219666 bytes
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Genre | |
Type | |
File Format |
application/pdf
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Language |
eng
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Date Available |
2009-04-09
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Provider |
Vancouver : University of British Columbia Library
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Rights |
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
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DOI |
10.14288/1.0051604
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Campus | |
Scholarly Level |
Graduate
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Aggregated Source Repository |
DSpace
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Item Media
Item Citations and Data
Rights
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.