Papers by Davy Van Nieuwenborgh
Answer Set Programming, 2005
The extended answer set semantics for simple logic programs, i.e. programs with only classical ne... more The extended answer set semantics for simple logic programs, i.e. programs with only classical negation, allows for the defeat of rules to resolve contradictions. In addition, a partial order relation on th e program's rules can be used to deduce a preference relation on its extended answer sets. In this paper, we propose a "quantitative" preference relation that associa tes
Computing Research Repository, 2007
Recently, there has been a lot of interest in the integration of Description Logics and rules on ... more Recently, there has been a lot of interest in the integration of Description Logics and rules on the Semantic Web. We define guarded hybrid knowledge bases (or g-hybrid knowledge bases) as knowl- edge bases that consist of a Description Logic knowledge base and a guarded logic program, similar to the DL+log knowledge bases from (Rosati 2006). G-hybrid knowledge bases enable
International Conference on Logic Programming/Joint International Conference and Symposium on Logic Programming, 2006
We present a formalism for logic program cooperation based on the answer set semantics. The syste... more We present a formalism for logic program cooperation based on the answer set semantics. The system consists of independent logic programs that are connected via a sequential communication channel. When presented with an input set of literals from its predecessor, a logic program computes its output as an answer set of itself, enriched with the input. It turns out that
European Conference on Artificial Intelligence, 2006
We present an approximation theory for the extended an- swer set semantics, using the concept of ... more We present an approximation theory for the extended an- swer set semantics, using the concept of an approximation constraint. Intuitively, an approximation constraint, while satisfied by a "per- fect" solution, may be left unsatisfied in an approximate ext ended answer set. Approximations improve as the number of unsatisfied constraints decreases. We show how the framework can also capture the classical
Practical Aspects of Declarative Languages, 2005
We describe the design of the OLPS system, an implementation of the preferred answer set semantic... more We describe the design of the OLPS system, an implementation of the preferred answer set semantics for ordered logic programs. The basic algorithm we propose computes the extended answer sets of a simple program using an intuitive 9-valued lattice, called T9. During the computation, this lattice is em- ployed to keep track of the status of the literals and the
Computational Logic in Multi-Agent Systems, 2006
We present a multi-agent formalism based on extended answer set programming. The system consists ... more We present a multi-agent formalism based on extended answer set programming. The system consists of independent agents connected via a com- munication channel, where knowledge and beliefs of each agent are represented by a logic program. When presented with an input set of literals from its prede- cessor, an agent computes its output as an extended answer set of its
Lecture Notes in Computer Science, 2004
The extended answer set semantics for logic programs allows for the defeat of rules to resolve co... more The extended answer set semantics for logic programs allows for the defeat of rules to resolve contradictions. We propose a refinement of these semantics based on a preference relation on extended literals. This relation, a strict partial order, induces a partial order on extended answer sets. The preferred answer sets, i.e. those that are minimal w.r.t. the induced order, represent the solutions that best comply with the stated preference on extended literals. In a further extension, we propose linearly ordered programs that are equipped with a linear hierarchy of preference relations. The resulting formalism is rather expressive and essentially covers the polynomial hierarchy. E.g. the membership problem for a program with a hierarchy of height n is Σ P n+1 -complete. We illustrate an application of the approach by showing how it can easily express hierarchically structured weak constraints, i.e. a layering of "desirable" constraints, such that one tries to minimize the set of violated constraints on lower levels, regardless of the violation of constraints on higher levels.
Answer Set Programming, 2005
We present extended conceptual logic programs (ECLPs) , for which reasoning is decidable and, mor... more We present extended conceptual logic programs (ECLPs) , for which reasoning is decidable and, moreover, can be reduced to finit e answer set pro- gramming. ECLPs are useful to reason with both ontological and rule-based knowledge, which is illustrated by simulating reasoning in an expressive descrip- tion logic (DL) equipped with DL-safe rules. Furthermore, ECLPs are more ex- pressive in
Logic Programming and Automated Reasoning/Russian Conference on Logic Programming, 2003
Abstract: We propose to regard a diagnostic system as an ordered logic theory,i.e. a partially or... more Abstract: We propose to regard a diagnostic system as an ordered logic theory,i.e. a partially ordered set of clauses where smaller rules carry more preference.
Reasoning Web, 2000
Open answer set programming combines the strengths of logic pro- gramming (a rule-based presentat... more Open answer set programming combines the strengths of logic pro- gramming (a rule-based presentation and a nonmonotonic seman- tics) and description logics (open domains). Reasoning under an open answer set semantics is undecidable in general, but decidabil- ity can be obtained for particular classes of logic programs , e.g., for bound guarded programs. In this paper, we show how bound
Logics in Artificial Intelligence, 2006
In this paper we show how the concepts of answer set programming and fuzzy logic can be succesful... more In this paper we show how the concepts of answer set programming and fuzzy logic can be succesfully combined into the single framework of fuzzy answer set programming (FASP). The framework offers the best of both worlds: from the answer set semantics, it inherits the truly declarative non-monotonic reasoning capabilities while, on the other hand, the notions from fuzzy logic
European Semantic Web Symposium / Conference, 2005
We present extended conceptual logic programs (ECLPs), for which reasoning is decidable and, more... more We present extended conceptual logic programs (ECLPs), for which reasoning is decidable and, moreover, can be reduced to finite answer set pro- gramming. ECLPs are useful to reason with both ontological and rule-based knowledge, which is illustrated by simulating reasoning in an expressive descrip- tion logic (DL) equipped with DL-safe rules. Furthermore, ECLPs are more ex- pressive in the sense
Rules and Rule Markup Languages for the Semantic Web, 2004
We extend Answer Set Programming with, possibly innite, open do- mains. Since this leads, in gene... more We extend Answer Set Programming with, possibly innite, open do- mains. Since this leads, in general, to undecidable reasoning, we restrict the syn- tax of programs, while carefully guarding useful knowledge representation mech- anisms such as negation as failure and inequalities. Reasoning with the resulting Conceptual Logic Programs can be reduced to nite, normal Answer Set Pro- gramming, for which
Lecture Notes in Computer Science, 2005
The extended answer set semantics for simple logic programs, i.e. programs with only classical ne... more The extended answer set semantics for simple logic programs, i.e. programs with only classical negation, allows for the defeat of rules to resolve contradictions. In addition, a partial order relation on the program's rules can be used to deduce a preference relation on its extended answer sets. In this paper, we propose a "quantitative" preference relation that associates a weight with each rule in a program. Intuitively, these weights define the "cost" of defeating a rule. An extended answer set is preferred if it minimizes the sum of the weights of its defeated rules. We characterize the expressiveness of the resulting semantics and show that it can capture negation as failure. Moreover the semantics can be conveniently extended to sequences of weight preferences, without increasing the expressiveness. We illustrate an application of the approach by showing how it can elegantly express subgraph isomorphic approximation problems, a concept often used in intelligence analysis to find specific regions of interest in a large graph of observed activities. a "qualitative" preference semantics is proposed, using a preference relation on rules, to induce a partial ordering on the extended answer sets of a program.
Lecture Notes in Computer Science, 2007
Fuzzy answer set programming has been introduced as a framework that successfully combines the co... more Fuzzy answer set programming has been introduced as a framework that successfully combines the concepts of answer set programming and fuzzy logic. In this paper, we show how the fuzzy answer set semantics can be mapped onto the semantics for HEX-programs, which are nonmonotonic logic programs under the answer set semantics that support the use of external function calls. By using the DLVHEX reasoning engine, we so devise a vehicle for effectively computing fuzzy answer sets.
Lecture Notes in Computer Science, 2007
We introduce the logic-based planning language K c as an extension of K . K c has two advantages ... more We introduce the logic-based planning language K c as an extension of K . K c has two advantages upon K. First, the introduction of external function calls in the rules of a planning description allows the knowledge engineer to describe certain planning domains, e.g. involving complex action effects, in a more intuitive fashion then is possible in K. Secondly, in contrast to the conformant planning framework K, K c is formalized as a conditional planning system, which enables K c to solve planning problems that are impossible to express in K, e.g. involving sensing actions. A prototype implementation of conditional planning with K c is build on top of the DLV K system, and we illustrate its use by some small examples.
Lecture Notes in Computer Science, 2005
Open answer set programming (OASP) is an extension of answer set programming where one may ground... more Open answer set programming (OASP) is an extension of answer set programming where one may ground a program with an arbitrary superset of the program's constants. We define a fixed point logic (FPL) extension of Clark's completion such that open answer sets correspond to models of FPL formulas and identify a syntactic subclass of programs, called (loosely) guarded programs. Whereas reasoning with general programs in OASP is undecidable, the FPL translation of (loosely) guarded programs falls in the decidable (loosely) guarded fixed point logic (µ(L)GF). Moreover, we reduce normal closed ASP to loosely guarded OASP, enabling a characterization of an answer set semantics by µLGF formulas. Finally, we relate guarded OASP to Datalog LITE, thus linking an answer set semantics to a semantics based on fixed point models of extended stratified Datalog programs. From this correspondence, we deduce 2-EXPTIME-completeness of satisfiability checking w.r.t. (loosely) guarded programs. C. Baral et al. (Eds.): LPNMR 2005, LNAI 3662, pp. 92-104, 2005. c Springer-Verlag Berlin Heidelberg 2005 Guarded Open Answer Set Programming 93
Lecture Notes in Computer Science, 2004
Often, decision making involves autonomous agents that are structured in a complex hierarchy, rep... more Often, decision making involves autonomous agents that are structured in a complex hierarchy, representing e.g. authority. Typically the agents share the same body of knowledge, but each may have its own, possibly conflicting, preferences on the available information. We model the common knowledge base for such preference agents as a logic program under the extended answer set semantics, thus allowing for the defeat of rules to resolve conflicts. An agent can express its preferences on certain aspects of this information using a partial order relation on either literals or rules. Placing such agents in a hierarchy according to their position in the decision making process results in a system where agents cooperate to find solutions that are jointly preferred. We show that a hierarchy of agents with either preferences on rules or on literals can be transformed into an equivalent system with just one type of preferences. Regarding the expressiveness, the formalism essentially covers the polynomial hierarchy. E.g. the membership problem for a hierarchy of depth n is Σ P n+2complete. We illustrate an application of the approach by showing how it can easily express a generalization of weak constraints, i.e. "desirable" constraints that do not need to be satisfied but where one tries to minimize their violation.
Lecture Notes in Computer Science, 2003
We equip ordered logic programs with negation as failure, using a simple generalization of the pr... more We equip ordered logic programs with negation as failure, using a simple generalization of the preferred answer set semantics for ordered programs. This extension supports a convenient formulation of certain problems, which is illustrated by means of an intuitive simulation of logic programming with ordered disjunction. The simulation also supports a broader application of "ordered disjunction", handling problems that would be cumbersome to express using ordered disjunction logic programs. Interestingly, allowing negation as failure in ordered logic programs does not yield any extra computational power: the combination of negation as failure and order can be simulated using order (and true negation) alone.
We introduce a framework, based on logic programming, for prefer- ential reasoning with agents on... more We introduce a framework, based on logic programming, for prefer- ential reasoning with agents on the Semantic Web. Initially, we encode the knowl- edge of an agent as a logic program equipped with call literals. Such call literals enable the agent to pose yes/no queries to arbitrary knowledge sources on the Semantic Web, without conditions on, e.g., the representation language of those sources. As conflicts may arise from reasoning with differen t knowledge sources, we use the extended answer set semantics, which can provide different strate- gies for solving those conflicts. Allowing, in addition, for an agent to express its preference for the satisfaction of certain rules over other s, we can then induce a preference order on those strategies. However, since it is n atural for an agent to believe its own knowledge (encoded in the program) but consider some sources more reliable than others, it can alternatively express pre ferences on call literals. Finally, we show how an agent ...
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Papers by Davy Van Nieuwenborgh