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 conflict resolution 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. Example production systems are OPS5, CLIPS, flex. (2005-06-17)