Rule-Based Expert Systems: Introduction and Fundamentals, Slides of Introduction to Computing

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CS613 INTRODUCTION TO

ARTIFICIAL INTELLIGENCE

Lecture 7

Rule-based expert systems

Today’s Class

• Introduction
  • History
  • intelligent systems
  • ES Structure
• Rule-based expert systems
• Uncertainty management in rule-based

expert systems

• Frame-based expert systems
• Knowledge Acquisition
• Knowledge engineering

Rule-based expert systems

• Introduction, or what is knowledge?
• Rules as a knowledge representation technique
• The main players in the development team
• Structure of a rule-based expert system
• Characteristics of an expert system
• Forward chaining and backward chaining
• Conflict resolution
• Summary

Introduction, or what is knowledge?

• Knowledge is a theoretical or practical

understanding of a subject or a domain.

Knowledge is also the sum of what is currently

known, and apparently knowledge is power.

Those who possess knowledge are called

experts.

• Anyone can be considered a domain expert if

he or she has deep knowledge (of both facts and

rules) and strong practical experience in a

particular domain. The area of the domain may

be limited. In general, an expert is a skilful

person who can do things other people cannot.

• The term rule in AI, which is the most

commonly used type of knowledge

representation, can be defined as an IF-

THEN structure that relates given information

or facts in the IF part to some action in the

THEN part. A rule provides some description

of how to solve a problem. Rules are

relatively easy to create and understand.

• Any rule consists of two parts: the IF part,

called the antecedent ( premise or

condition ) and the THEN part called the

consequent ( conclusion or action ).

Rules as a knowledge representation

technique

IF antecedent THEN consequent

• A rule can have multiple antecedents joined by the keywords AND ( conjunction ), OR ( disjunction ) or a combination of both.

IF antecedent 1  IF antecedent 1  AND antecedent. 2  OR antecedent (^2).  .. .. AND antecedent n  OR antecedent n  THEN consequent THEN consequent

Rules can represent relations,

recommendations, directives, strategies

and heuristics:

• Relation IF the ‘fuel tank’ is empty THEN the car is dead
• Recommendation IF the season is autumn AND the sky is cloudy AND the forecast is drizzle THEN the advice is ‘take an umbrella’
• Directive IF the car is dead AND the ‘fuel tank’ is empty THEN the action is ‘refuel the car’

• Strategy

IF the car is dead THEN the action is ‘check the fuel tank’; step1 is complete

IF step1 is complete AND the ‘fuel tank’ is full THEN the action is ‘check the battery’; step2 is complete

• Heuristic

IF the spill is liquid AND the ‘spill pH’ < 6 AND the ‘spill smell’ is vinegar THEN the ‘spill material’ is ‘acetic acid’

The main players in the development team

Expert System

End-user

Domain Expert Knowledge Engineer Programmer

Project Manager

Expert System Development Team

• The domain expert is a knowledgeable

and skilled person capable of solving problems in a specific area or domain. This person has the greatest expertise in a given domain. This expertise is to be captured in the expert system. Therefore, the expert must be able to communicate his or her knowledge, be willing to participate in the expert system development and commit a substantial amount of time to the project. The domain expert is the most important player in the expert system development team.

• The programmer is the person

responsible for the actual programming, describing the domain knowledge in terms that a computer can understand. The programmer needs to have skills in symbolic programming in such AI languages as LISP, Prolog and OPS and also some experience in the application of different types of expert system shells. In addition, the programmer should know conventional programming languages like C, Pascal, FORTRAN and Basic.

• The project manager is the leader of the expert system development team, responsible for keeping the project on track. He or she makes sure that all deliverables and milestones are met, interacts with the expert, knowledge engineer, programmer and end-user.
• The end-user , often called just the user , is a person who uses the expert system when it is developed. The user must not only be confident in the expert system performance but also feel comfortable using it. Therefore, the design of the user interface of the expert system is also vital for the project’s success; the end-user’s contribution here can be crucial.

Production system model

Conclusion

REASONING

Long-term Memory

Production Rule

Short-term Memory

Fact

Basic structure of a rule-based

expert system

Inference Engine

Knowledge Base

Rule: IF-THEN

Database

Fact

Explanation Facilities

User Interface

User