Processing Indefinite Deductive Databases under the Possible Model Semantics

The relationship between possible and supported models of unstratified indefinite deductive databases is studied, when disjunction is interpreted inclusively. Possible and supported models are shown to coincide under a suitable definition of supportedness, and the concept of a supported cover is introduced and shown to characterise possible models and facilitate top-down query processing and compilation under the possible model semantics. The properties and query processing of deductive databases under the possible model semantics is compared and contrasted with the perfect model semantics.