We propose and study extensions of logic programming with constraints represented as generalized atoms of the form C(X), where X is a finite set of atoms and C is an abstract constraint (formally, a collection of sets of atoms). Atoms C(X) are satisfied by an interpretation (set of atoms) M , if M C. We focus here on monotone constraints, that is, those collections C that are closed under the superset. They include, in particular, weight (or pseudo-boolean) constraints studied both by the logic programming and SAT communities. We show that key concepts of the theory of normal logic programs such as the one-step provability operator, the semantics of supported and stable models, as well as several of their properties including complexity results, can be lifted to such case.

All major semantics of normal logic programs and normal logic programs with aggregates can be described as fixpoints of the one-step provability operator or of operators that can be derived from it. No such systematic operator-based approach to semantics of disjunctive logic programs has been developed so far. This paper is the first step in this direction. We formalize the concept of one-step-provability for disjunctive logic programs by means of non-deterministic operators on the lattice of interpretations. We establish characterizations of models, minimal models, supported models and stable models of disjunctive logic programs in terms of pre-fixpoints and fixpoints of non-deterministic immediateconsequence operators and their extensions to the four-valued setting. We develop our results for programs in propositional language extended with monotone aggregate atoms. For the most part, our concepts, results and proof techniques are algebraic, which opens a possibility for further generalizations to the abstract algebraic setting of non-deterministic operators on complete lattices.

Managing uncertainty and/or vagueness is starting to play an important role in Semantic Web representation languages. Our aim is to overview basic concepts on representing uncertain and vague knowledge in current Semantic Web ontology and rule languages (and their combination).

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Abstract. We investigate mca-programs, that is, logic programs with clauses built of monotone cardinality atoms of the form kX, where k is a non-negative integer and X is a finite set of propositional atoms. We develop a theory of mca-programs. We demonstrate that the operational concept of the one-step provability operator generalizes to mca-programs, but the generalization involves nondeterminism. Our main results show that the formalism of mca-programs is a common generalization of (1) normal logic programming with its semantics of models, supported models and stable models, (2) logic programming with cardinality atoms and with the semantics of stable models, as defined by Niemelä, Simons and Soininen, and (3) of disjunctive logic programming with the possiblemodel semantics of Sakama and Inoue. 1

We study properties of programs with monotone and convex constraints. We extend to these formalisms concepts and results from normal logic programming. They include the notions of strong and uniform equivalence with their characterizations, tight programs and Fages Lemma, program completion and loop formulas. Our results provide an abstract account of properties of some recent extensions of logic programming with aggregates, especially the formalism of lparse programs. They imply a method to compute stable models of lparse programs by means of off-the-shelf solvers of pseudo-boolean constraints, which is often much faster than the smodels system. 1

This note provides background information and references to the tutorial on recent research developments in logic programming inspired by need of knowledge representation.

All major semantics of normal logic programs and normal logic programs with aggregates can be described as fixpoints of the one-step provability operator or of operators that can be derived from it. No such systematic operator-based approach to semantics of disjunctive logic programs has been developed so far. This paper is the first step in this direction.

We show that the concept of strong equivalence of logic programs can be generalized to an abstract algebraic setting of operators on complete lattices. Our results imply characterizations of strong equivalence for several nonmonotonic logics including logic programming with aggregates, default logic and a version of autoepistemic logic.

and uniform equivalence of nonmonotonic theories — an algebraic