ExpertSystem Modified

8/22/2019 ExpertSystem Modified

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An expert system is a computer program thatis designed to hold the accumulated

knowledge of one or more domain experts


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What is an Expert System (ES)? Relies on internally represented knowledge to perform

tasks

Utilizes reasoning methods to derive appropriate new

knowledge

Usually restricted to a specificproblem domain

Some systems try to capture common-sense

knowledge


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Definitions Expert System a computer system that emulates the decision-making

ability of a human expert in a restricted domain.

An intelligent computer program that uses knowledge

and inference procedures to solve problems that are

difficult enough to require significant human expertise

for their solutions.


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Main Components of an ES

Knowledge Base

Inference Engine

Expertise

Expertise

Facts / Information


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ES Components knowledge base

contains essential information about the problemdomain

often represented as facts and rules

inference engine

mechanism to derive new knowledge from the

knowledge base and the information provided by theuser

often based on the use of rules


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General Concepts and

Characteristics of ES

knowledge representation

inference

knowledge acquisition

explanation


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When to Use ESs expert systems are not suitable for all types of domains

and tasks

conventional algorithms are known and efficient the main challenge is computation, not knowledge

knowledge cannot be captured easily

users may be reluctant to apply an expert system to a

critical task


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ES Tools ES languages

higher-level languages specifically designed for

knowledge representation and reasoning SAIL, KRL, KQML

shells

an ES development tool/environment where the userprovides the knowledge base


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ES Elements knowledge base

inference engine

working memory agenda

explanation facility

knowledge acquisition facility

user interface


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ES StructureKnowledge Base

Inference Engine

Working Memory

UserInterfac

e

Knowledge

Acquisition

Facility

ExplanationFacility

Agenda


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Rule-Based ES

knowledge is encoded as IF THEN rules

these rules can also be written asproduction rules

the inference engine determines which rule antecedents

are satisfied the left-hand side must match a fact in the working

memory

satisfied rules are placed on the agenda

rules on the agenda can be activated (fired) an activated rule may generate new facts through its

right-hand side

the activation of one rule may subsequently cause theactivation of other rules


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Example RulesIF THEN Rules

Rule: Red_Light

IF the light is red

THEN stop

Rule: Green_Light

IF the light is green

THEN go

antecedent

(left-hand-side)

consequent

(right-hand-side)

Production Rules

the light is red ==> stop

the light is green ==> go

antecedent (left-hand-side)

consequent

(right-hand-side)


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Foundations of Expert SystemsRule-Based Expert Systems

Knowledge BaseInference Engine

RulesPattern

MatchingFacts

Rete

Algorithm

Markov

Algorithm

Post

ProductionRules

Conflict

Resolution

Action

Execution


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ES Advantages

economical lower cost per user

availability

accessible anytime, almost anywhere response time

often faster than human experts

reliability can be greater than that of human experts

no distraction, fatigue, emotional involvement, explanation

reasoning steps that lead to a particular conclusion

intellectual property cant walk out of the door


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Components of an Expert

System The knowledge base is the collection of facts and

rules which describe all the knowledge about theproblem domain

The inference engine is the part of the systemthat chooses which facts and rules to apply whentrying to solve the users query

The user interface is the part of the system whichtakes in the users query in a readable form andpasses it to the inference engine. It then displaysthe results to the user.


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Why use Expert Systems?

Experts are not alwaysavailable. An expert system canbe used anywhere, any time.

Human experts are not 100%reliable or consistent.

Experts may not be good atexplaining decisions

Cost effective


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Problems with Expert Systems

Limited domain

Systems are not always up todate, and dont learn

No commonsense

Experts needed to setup andmaintain system


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Legal and Ethical Issues

Who is responsible if the advice is wrong?

The user?

The domain expert?

The knowledge engineer?

The programmer of the expert system shell?

The company selling the software?


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ExpertSystem Modified

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