379 research outputs found
Loop Formulas for Description Logic Programs
Description Logic Programs (dl-programs) proposed by Eiter et al. constitute
an elegant yet powerful formalism for the integration of answer set programming
with description logics, for the Semantic Web. In this paper, we generalize the
notions of completion and loop formulas of logic programs to description logic
programs and show that the answer sets of a dl-program can be precisely
captured by the models of its completion and loop formulas. Furthermore, we
propose a new, alternative semantics for dl-programs, called the {\em canonical
answer set semantics}, which is defined by the models of completion that
satisfy what are called canonical loop formulas. A desirable property of
canonical answer sets is that they are free of circular justifications. Some
properties of canonical answer sets are also explored.Comment: 29 pages, 1 figures (in pdf), a short version appeared in ICLP'1
Reconciling Well-Founded Semantics of DL-Programs and Aggregate Programs
Logic programs with aggregates and description logic programs (dl-programs) are two recent extensions to logic programming. In this paper, we study the relationships between these two classes of logic programs, under the well-founded semantics. The main result is that, under a satisfaction-preserving mapping from dl-atoms to aggregates, the well-founded semantics of dl-programs by Eiter et al., coincides with the well-founded semantics of aggregate programs, defined by Pelov et al. as the least fixpoint of a 3-valued immediate consequence operator under the ultimate approximating aggregate. This result enables an alternative definition of the same well-founded semantics for aggregate programs, in terms of the first principle of unfounded sets. Furthermore, the result can be applied, in a uniform manner, to define the well-founded semantics for dl-programs with aggregates, which agrees with the existing semantics when either dl-atoms or aggregates are absent
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