
90 Chapter 3 DevelopingKnowleDge-BaseDsystems
JESS can be used in two overlapping ways. First, it can be a rule en-
gine—that is, a special kind of program that efficiently applies rules to data.
A rule-based program can have thousands of rules, and JESS will continu-
ally apply them to data in the form of a knowledge base. In general, the rules
represent the heuristic knowledge of a human expert in a domain, and the
knowledge base represents the state of an evolving situation.
JESS is also a general-purpose programming language; thus, it can di-
rectly access all Java classes and libraries. For this reason, JESS is frequently
used as a