Handling disjunctions in open world relational databases

Incomplete information is usually present in a database in the form of null values. Several other forms of incompleteness such as fuzzy information, partial values and disjunctive information have been studied extensively. Most of the research on indefinite information has been carried out under the Closed World Assumption(CWA). In this paper, we present a data structure that supports the opposite view, the Open World Assumption(OWA), where negative information is explicitly represented in a relation. We allow disjunctions at the tuple level to appear in two forms: A or B and notA or notB, thus obtaining a gain in expressivity. Wenot define a generalization of the relational algebra that handles this kind of information.