It was developed by Ernest Friedman-Hill of Sandia National Laboratories.
[1] In recent years, intelligent agent systems have also developed, which depend on a similar ability.
Rather than a procedural paradigm, where one program has a loop that is activated only one time, the declarative paradigm used by Jess applies a set of rules to a set of facts continuously by a process named pattern matching.
Rules can modify the set of facts, or can execute any Java code.
In contrast, CLIPS, which is the basis and starting code for Jess, is free and open-source software.