Specifying Closed World Assumptions for Logic Databases

Closed world assumptions” (CWAs) are an important class of implicit completions for logic databases. We present a new general definition of CWA; it is parameterized, so that known and new versions of CWAs can be derived as special cases. Our CWA, in turn, instantiates the more basic notion of “database completion” and satisfies natural properties. It can even be characterized by the property of determining maximal completions without generating too much new information. We study syntactic as well as semantic definitions and prove them to be equivalent. By discussing several instances of CWAs we demonstrate the applicability of our framework to database specification.