1. A method of executing a rule in a system having a rule base for storing rules each including a condition part, an action descriptor part, files for storing object data, and a user interface means comprising the steps of: setting a value to a flag indicating whether a rule having said flag is to be automatically activated or not, said flag being included in a trigger descriptor part provided in at least one rule of the rules stored in said rule base, said trigger descriptor part being a third part included in the rule in addition to said condition part and said action descriptor part; specifying timing data to said at least one rule, for retrieving object data through said user interface means; fetching, when a current timing matches with the specified timing data a rule whose flag indicates the value that the rule having said flag to be automatically activated; fetching object data which satisfies the condition part defined in the fetched rule; and executing a process defined in the action descriptor part of the rule with the fetched object data.