Structure of rule-based expert system

• In the early seventies, Newell and Simon from Carnegie-Mellon University proposed a production system model, the foundation of the modern rule-based expert systems.
• The production model is based on the idea that humans solve problems by applying their knowledge (expressed as production rules) to a given problem represented by problem-specific information.
• The production rules are stored in the long-term memory and the problem-specific information or facts in the short-term memory.

The Knowledge base

• The knowledge base contains the domain knowledge useful for problem solving.
• In rule-based expert system, the knowledge is represented as a set of rules. Each rule specifies a relation, recommendation, directive, strategy or heuristic and has the IF (condition) THEN (action) structure.
• When the condition part of a rule is satisfied, the rule is said to fire and the action part is executed. 

Database

• The database includes a set of facts used to match against the IF (condition) parts of rules stored in the knowledge base.

Inference engine

• The inference engine carries out the reasoning whereby the expert system reaches a solution.
• It links the rules given in the knowledge base with the facts provided in the database.

Explanation facilities

• The explanation facilities enable the user to ask the expert system how a particular conclusion is reached and why a specific fact is needed.
• An expert system must be able to explain its reasoning and justify its advice, analysis or conclusion.

User interface

• The user interface is the means communication between a user seeking a solution to the problem and an expert system.

Complete structure of a rule-based expert system

 

Expert System Shells

• The Expert System shell simplifies the process of creating knowledge base.
• It is the shell that actually processes the information entered by a user relates it to the concepts contained in the knowledge base and provides an assessment or solution for a particular problem.
• The E.S shell provides a layer between the user interface and the computer O.S to manage the input and output of the data.
• It also manipulates the information provided by the user in conjunction with the knowledge base to arrive at a particular conclusion.