Production systems use the same basic IF-THEN format to represent knowledge in very different domains. An informal Automated Tourist Guide rule, for example, expresses a very different content from the rules, given earlier, for closing Tweetie’s cage or for applying suntan lotion:

rule centre_theatre

condition:

[entertainment type theatre] and

[entertainment place centre]

action:

add: [location piccadilly circus]

Yet all three rules have the same underlying form: whether its function is to infer conclusions from premises or to perform actions in response to given circumstances, in each case the `condition’ side of the rule is matched against working memory and, if the match succeeds, the action specified in the rule body is executed.