Forward chaining rules consist of a condition part and an action part. The condition part contains conditions which are matched against the object base. If and only if all the conditions are matched, the rule may fire. If the rule is selected to fire, the actions it performs are given in the action part of the rule. The process of selecting and firing a rule is known as the Forward Chaining Cycle, and the forward chaining engine cycles repeatedly until it runs out of rules or a rule instructs it to stop. KnowledgeWorks forward chaining rules reside in a group of rules, or context, and may have a priority number associated with them for conflict resolution (choosing which of a set of eligible rules may fire).
KnowledgeWorks and Prolog User Guide (Unix version) - 6 Dec 2011