Expert Systems - Digital Signal Processing in Power System Protection and Control - page 294

Fig. 14.1 Data versus
knowledge processing

Data Processing Knowledge Processing

Algorithmic
Methods

Intelligent
Searches

Know-
ledge

Data

Knowledge
Base Base

Inference

Solution

Engine

Data
Base

Fig. 14.2 Structure of an expert system

Nevertheless, they have been found useful and are quite often applied, also for
power system problems, including protection and control issues.

14.1 Components of an Expert System

An ES is usually organized as it is schematically shown in Fig. 14.2 . The
components of ES are:

• Knowledge base—containing the knowledge about the system, its functioning,
rules of problem solving, etc,
• Data base—including the facts, which generally describe the domain and the
state of the problem to be solved,
• Inference Engine—with the reasoning principles and conflict resolution

strategies.

The block connections in Fig. 14.2 suggest that there exist unidirectional (read-
only) information flow from the KB to the Inference Engine and bidirectional
exchange of data with the DB. This is because during data and knowledge
processing new facts are created that should be stored in the Data Base for further
usage.
The most important blocks of the ES structure, i.e., Knowledge Base and
Inference Engine contain the information provided by human experts. Potential
experts are those who possess knowledge and strong practical experience in
particular domain. They are often skillful persons who can do things that other
people cannot. The experts should, however, be capable of expressing their
knowledge in the form of rules for problem solving, which is not always simple