Counterfactual exceptions in deductive database queries

Troels Andreasen and Henning Christiansen
Department of Computer Science
Roskilde University, P.O.Box 260, DK-4000 Roskilde, Denmark

This paper suggests a new construct to capture negative hypothesis in database query languages. Counterfactual exceptions, as the construct is called, are specialized constraints in queries, that serve as means to suppress part of the database. The expressibility obtained is closely related to what is captured by possible world counterfactuals, but the semantic characterization becomes simpler and an implementation can be obtained in a straightforward way. The logical semantics is described in terms of model and completion constructions. An inference system is obtained by a modification of modus ponens. Also a generalization into a language with hypothetical implication goals and positive as well as negative hypotheses is suggested.

See pdf.

12th European Conference on on Artificial Intelligence, ECAI'96, August 11-16,1996, Budapest, Hungary. pp. 340-344.