Expert systems: Introduction: An expert system is a set of programs that manipulate encoded knowledge to solve problems in a specialized domain that normally requires human expertise. An expert system’s knowledge is obtained form expert sources and coded in a form suitable for the system to use in its interference or reasoning processes. The expert knowledge must be obtained from specialists or other sources of expertise, such as texts, journal articles, and data bases. This type of knowledge usually requires much training and experience in some specialized field such as medicine, geology, system configuration, or engineering design. Characteristic Features of Expert systems: Expert systems differ from conventional computer systems in several important ways. 1. Expert systems use knowledge rather than data to control the solution process. Much of the knowledge used is heuristic in nature rather than algorithmic. 2. The knowledge is encoded and maintained as an entity separate from the control program. As such, it is not compiled together with the control program itself. This permits the incremental addition and modification
(refinement) of the knowledge base without recompilation of the control programs. Furthermore, it is possible in some cases to use different knowledge bases with the same control programs to produce different types of expert systems. 3. Expert systems are capable of explaining how a particular conclusion was reached, and why requested information is needed during a consultation. This is important as it gives the user a chance to assess and understand the system’s reasoning ability, thereby improving the user’s confidence in the system. 4. Expert systems use symbolic representations for knowledge (rules, networks, or frames) and perform their interference through symbolic computations that closely resemble manipulations of natural language. Expert and Systems analyst Development engine Inference engine User interface Knowledge Base Proble m Doma in User
Fig. An expert system model Rule-Based System Architectures: The most common form of architecture used in expert and other types of knowledge based systems is the production system, also called the rule-based system. This type of system uses knowledge encoded in the form of production rules, that is, if … then rules. IF: Condition-1 and Condition-2 and Condition-3 THEN Take Action-4 IF: The temperature is greater than 200 degrees, and the water level is low THEN: Open the safety valve. A&B & C&D E&F Each rule represents a small chunk of knowledge relating to the given domain of expertise which leads from some initially known facts to some useful conclusions or action part of the rule is then accepted as known(or at least known with some degree of certainty).
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