Logic Programs Viewed as Modular Speciications

In this paper, we add a module system to supernormal default speciications (which have a circumscription-like \minimal model" semantics). Our intention is to formalize that certain rules deene certain elementary facts; we do not consider the more syntactical side of modules (such as the hiding of names). Logic programs can be naturally translated into this system by taking the head literal as the deened part of a rule. Our main results are criteria for the equivalence of a logic program and a modular speciication. Our approach explicitly contains the module information given by logic programming rules, so it should lead to a better understanding of their semantics. Additionally, it can be seen as a common generalization of logic programming and supernormal default logic; it supports the knowledge representation features of both.