Degrees of Exclusivity in Disjunctive Databases

Ever since the emergence of the relational database model, the problem of incompleteness has been studied extensively. Declarative semantics for disjunctive databases widely adopt two methodologies representing opposite ends of the spectrum - Minker's GCWA interprets disjunctions exclusively while Ross and Topor's DDR interprets them inclusively. We argue that the use of either one as the semantics is limiting. For example, in a blood group relation, saying that the blood group of John is A or B, BG(John,A) ∨ BG(John,B) can be interpreted exclusively while the statement supplier S1 supplies part P1 or P2 to project J1, supplies(S1, P1, J1) ∨ supplies(S1, P2, J1) need not necessarily be exclusive. In this paper, we present a model that allows the nature of the disjunctions to be represented explicitly and show its relation to other semantics for disjunctive databases. A notable feature of this extension is that it does not require variables in order to represent indefinite information.