Mode-directed preferences for logic programs

Preference logic programming (PLP) is an extension of constraint logic programming for declaratively specifying problems requiring optimization or comparison and selection among alternative solutions to a query. PLP essentially separates the programming of a problem itself from the criteria specification of its solution selection. In this paper we provide a syntax for PLP based upon mode-directed preferences and a semantics based upon Herbrand models and fixed-point theory. Our method uses mode declarations to designate certain predicates as optimization predicates, and uses preference rules for stating the criteria for determining their optimal solutions. This paper also presents an elegant and easy method of executing preference logic programs in terms of tabled Prolog. Automatic transformation is applied to embed the preferences into the problem specification for efficient evaluation. We show that the procedural semantics of a preference logic program is equivalent to its declarative semantics.