A production system consists of a collection of productions

(rules), a working memory of facts and an algorithm

known as forward chaining for producing new facts from old.

A rule becomes eligible to "fire" when its conditions match

some set of elements currently in working memory. A conflictresolution strategy determines which of several eligible

rules (the conflict set) fires next. A condition is a list

of symbols which represent constants, which must be matched

exactly; variables which bind to the thing they match and "

symbol" which matches a field not equal to symbol. Examples

are OPS5, CLIPS, flex.