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.