Modular Speciications with Supernormal Defaults ?

We add a simple module system to speciications with super-normal defaults. It allows to distinguish between \deening" and \calling" occurrences of predicates. This greatly improves the understandability of large default speciications and especially helps to solve the problem of unwanted contrapositions of rules. Our approach is similar to the distinction between head and body of logic programming rules, but it works on the higher level of default theories. So our results can help to integrate both approaches | at least on the semantical side for speciication purposes. We also clarify the relation to prioritized defaults and argue that modular speciications are often preferable. Finally, we give a theoretical basis for query evaluation.