CS62S: Expert Systems

Based on:

The Engineering of Knowledge-based Systems: Theory and PracticeA. J. Gonzalez and D. D. Dankel

Introduction to Knowledge-based Systems

General problem solving knowledge Intelligent program

Inference engine Knowledge base Data / Fact base

Separation of knowledge from its use

For a new problem domain – change knowledge base

Knowledge Representation

Logic Rules Associative (semantic) networks Frames Objects

Traditional Computer Programming

Structured sequence of steps

Algorithm

Finite amount of time

Search – alternative to algorithmic solution

Path connecting problem to the solution

Problem space Procedurally defined Network Tree

Solution space (problem space examined)

Search Methods

Random

Blind

Directed

Search Types

Depth-first Breath-first Beam Hill-climbing Branch and bound Best-first A* (best-first and branch and bound)

Heuristics vs. algorithm

Specific knowledge Rule of thumb Prior knowledge Expertise Timely solution Estimation

Gonzalez and Dankel describes knowledge-based systems as:

“A computerized system that uses knowledge about some domain to arrive at a solution to a problem from that domain. This solution is essentially the same as that concluded by a person knowledgeable about the domain of the problem when confronted with the same problem“

Expert systems

Separation of knowledge from how it is used

Use of highly specific domain knowledge

Heuristic rather than algorithms

MYCIN

Used to diagnose blood disorderIncorporates all three elements

Types of expertise

Associational

The internal workings of a system are not understood. The behaviour is used to solve problems

Motor skills expertise

Practice makes perfect (sports, physical tasks, etc)

Theoretical expertise

The internal workings of a device or system are well understood. The expert can solve problems never seen before.

Advantages of Expert Systems

Wide distribution of scarce expertise Ease of modification Consistency of answers Perpetual accessibility Preservation of expertise Solution of Problem involving

incomplete data Explanation of solution

Disadvantages

Answers may not always be correct

Knowledge limited to the domain of expertise

Lack of common sense

Expert systems architecture

User

Knowledge engineer

Tool builder