Page 116 - DCAP310_INTRODUCTION_TO_ARTIFICIAL_INTELLIGENCE_AND_EXPERT_SYSTEMS

Introduction to Artificial Intelligence & Expert Systems

Notes Self Assessment

State whether the following statements are true or false:
13. Deductive inference is monotonic.
14. AI research is not technical and specialized, deeply divided into subfields that often fail to
communicate with each other.

6.8 Truth Maintenance System (TMS)

Truth Maintenance Systems, also called Reason Maintenance Systems, are used within Problem
Solving Systems, in conjunction with Inference Engines (IE) such as rule-based inference systems,
to manage as Dependency Network the inference engine’s beliefs in given sentences.

PROBLEM SOLVING SYSTEM
+-----------------------------------------------+
| +----+ +------+ |
| | IE |<--------------->| TMS | |
| +----+ +------+ |
+-----------------------------------------------+
A TMS is intended to satisfy a number of goals:

Provide Justifications for Conclusions

When a problem solving system gives an answer to a user’s query, an explanation of the answer
is usually required. If the advice to a stockbroker is to invest millions of dollars, an explanation
of the reasons for that advice can help the broker reach a reasonable decision.

Notes An explanation can be constructed by the IE by tracing the justification of the
assertion.

Recognise Inconsistencies

The IE may tell the TMS that some sentences are contradictory. Then, if on the basis of other IE
commands and of inferences we find that all those sentences are believed true, then the TMS
reports to the IE that a contradiction has arisen. The IE can eliminate an inconsistency by
determining the assumptions used and changing them appropriately, or by presenting the
contradictory set of sentences to the users and asking them to choose which sentence(s) to
retract.

Support Default Reasoning

In many situations we want, in the absence of firmer knowledge, to reason from default
assumptions. If Tweety is a bird, until told otherwise, we will assume that Tweety flies and use
as justification the fact that Tweety is a bird and the assumption that birds fly.

Remember Derivations Computed Previously

In the process of determining what is responsible for a network problem, we may have derived,
while examining the performance of a name server, that Ms. Doe is an expert on e-mail systems.

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