1. A rule based document generation system for constructing insurance policies in response to coverage information input thereto, comprising: a computer processor; first memory means coupled to said processor, said first memory means storing a library of rule sets each corresponding to a different insurance policy clause and designating a set of parameters that must be satisfied in order for its corresponding insurance policy clause to be included in an insurance policy; a user interface coupled to said processor for enabling a user to enter coverage information identifying a set of different coverages to be provided in an insurance policy; said processor being adapted to compare the parameters designated by the rule sets for the insurance policy clauses to the set of different coverages identified by said coverage information, to provide a list of those rule sets having parameters that are all satisfied by said coverage information; means for identifying superseded insurance policy rule sets referred to on said list and replacing the superseded insurance policy rule sets referred to on said list with references to superseding endorsement rule sets each corresponding to a different endorsement clause; and means for assembling the insurance policy and endorsement clauses corresponding to the rule sets referred to on said list into said insurance policy.