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Rules and ontologies for the Semantic Web
, 2008
"... Abstract. Rules and ontologies play a key role in the layered architecture of the Semantic Web, as they are used to ascribe meaning to, and to reason about, data on the Web. While the Ontology Layer of the Semantic Web is quite developed, and the Web Ontology Language (OWL) is a W3C recommendation s ..."
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Abstract. Rules and ontologies play a key role in the layered architecture of the Semantic Web, as they are used to ascribe meaning to, and to reason about, data on the Web. While the Ontology Layer of the Semantic Web is quite developed, and the Web Ontology Language (OWL) is a W3C recommendation since a couple of years already, the rules layer is far less developed and an active area of research; a number of initiatives and proposals have been made so far, but no standard as been released yet. Many implementations of rule engines are around which deal with Semantic Web data in one or another way. This article gives a comprehensive, although not exhaustive, overview of such systems, describes their supported languages, and sets them in relation with theoretical approaches for combining rules and ontologies as foreseen in the Semantic Web architecture. In the course of this, we identify desired properties and common features of rule languages and evaluate existing systems against their support. Furthermore, we review technical problems underlying the integration of rules and ontologies, and classify representative proposals for theoretical integration approaches into different categories. 1
Answer set programming with functions
 In Proc. KR’08
, 2008
"... To compute a function such as a mapping from vertices to colors in the graph coloring problem, current practice in Answer Set Programming is to represent the function as a relation. Among other things, this often makes the resulting program unnecessarily large when instantiated on a large domain. Th ..."
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Cited by 18 (1 self)
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To compute a function such as a mapping from vertices to colors in the graph coloring problem, current practice in Answer Set Programming is to represent the function as a relation. Among other things, this often makes the resulting program unnecessarily large when instantiated on a large domain. The extra constraints needed to enforce the relation as a function also make the logic program less transparent. In this paper, we consider adding functions directly to normal logic programs. We show that the answer set semantics can be generalized to these programs straightforwardly. We also show that the notions of loops and loop formulas can be extended, and that through program completion and loop formulas, a normal logic program with functions can be transformed to a Constraint Satisfaction problem.
M.: FDNC: Decidable nonmonotonic disjunctive logic programs with function symbols
 ACM TOCL
, 2010
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Disjunctive ASP with functions: Decidable queries and effective computation. TPLP
, 2010
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On the Termination of Logic Programs with Function Symbols
 IN DOVIER, A., & SANTOS COSTA, V. (EDS.), PROC. OF THE 8TH INT
, 2012
"... Recently there has been an increasing interest in the bottomup evaluation of the semantics of logic programs with complex terms. The main problem due to the presence of functional symbols in the head of rules is that the corresponding ground program could be infinite and that finiteness of models a ..."
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Recently there has been an increasing interest in the bottomup evaluation of the semantics of logic programs with complex terms. The main problem due to the presence of functional symbols in the head of rules is that the corresponding ground program could be infinite and that finiteness of models and termination of the evaluation procedure is not guaranteed. This paper introduces, by deeply analyzing program structure, new decidable criteria, called safety and Γacyclicity, for checking termination of logic programs with function symbols under bottomup evaluation. These criteria guarantee that stable models are finite and computable, as it is possible to generate a finitely ground program equivalent to the source program. We compare new criteria with other decidable criteria known in the literature and show that the Γacyclicity criterion is the most general one. We also discuss its application in answering bound queries.
Bidirectional Answer Set Programs with Function Symbols
, 2009
"... Current Answer Set Programming (ASP) solvers largely build on logic programming without function symbols. This limitation makes ASP decidable, but greatly complicates the modeling of indefinite time, recursive data structures (e.g., lists), and infinite processes and objects in general. Recent resea ..."
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Cited by 2 (1 self)
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Current Answer Set Programming (ASP) solvers largely build on logic programming without function symbols. This limitation makes ASP decidable, but greatly complicates the modeling of indefinite time, recursive data structures (e.g., lists), and infinite processes and objects in general. Recent research thus aims at finding decidable fragments of ASP with function symbols and studying their complexity. We identify bidirectional ASP programs as an expressive such fragment that is useful, e.g., for reasoning about actions involving both the future and the past. We tightly characterize the computational complexity of bidirectional programs and of some of their subclasses, addressing the main reasoning tasks. Our results also imply that the recently introduced FDNC programs can be extended by inverse predicates while retaining decidability, but computational costs are unavoidably higher.
Weight Constraint Programs with Functions
"... Abstract. In this paper we consider a new class of logic programs, called weight constraint programs with functions, which are lparse programs incorporating functions over nonHerbrand domains. We define answer sets for these programs and develop a computational mechanism based on loop completion. W ..."
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Abstract. In this paper we consider a new class of logic programs, called weight constraint programs with functions, which are lparse programs incorporating functions over nonHerbrand domains. We define answer sets for these programs and develop a computational mechanism based on loop completion. We present our results in two stages. First, we formulate loop formulas for lparse programs (without functions). Our result improves the previous formulations in that our loop formulas do not introduce new propositional variables, nor there is a need of translating lparse programs to nested expressions. Building upon this result we extend the work to weight constraint programs with functions. We show that the loop completion of such a program can be transformed to a Constraint Satisfaction Problem (CSP) whose solutions correspond to the answer sets of the program, hence offtheshelf CSP solvers can be used for answer set computation. We show some preliminary experimental results. 1
On the decidability of FDNC programs
 IL MILIONE: A JOURNEY IN THE COMPUTATIONAL LOGIC IN ITALY
"... We provide a new decidability proof for the consistency of FDNC programs under the stable model semantics, based on regular splitting sequences. With this technique, we can slightly relax the definition of FDNC programs and make a first step towards a precise understanding of the relationships bet ..."
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We provide a new decidability proof for the consistency of FDNC programs under the stable model semantics, based on regular splitting sequences. With this technique, we can slightly relax the definition of FDNC programs and make a first step towards a precise understanding of the relationships between FDNC programs and finitely recursive programs.