3.2 Expert System Structure
Expert system consists of some main modules which are
relatively independent and have their own functions. The
basic structure contains the following several parts [11].
1) Knowledge Base
Knowledge Base is memory areas of knowledge and
experience, including field facts and heuristic knowledge.
The field facts are wide field of knowledge, and usually
referred to the knowledge and common sense written in the
books. But the heuristic knowledge is a field in which we
can ensure correct realization, judge knowledge correctly,
and observe knowledge by experience. In the expert
system, knowledge is a major factor, which decides system
performance whether is superior or not .It can be described
as that the expert system is equal to knowledge and
reasoning. According to the knowledge engineering theory,
the reasoning ability of an expert system depends on three
characteristics of knowledge base. There are usability,
certainty and perfection. The usability and certainty of
knowledge depends on the field experts. However, the
availability of knowledge is relation to field experts and
knowledge engineers.