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- Nicola Leone, Gerald Pfeifer, +4 authors Francesco Scarcello
- ACM Trans. Comput. Log.
- 2006

Disjunctive Logic Programming (DLP) is an advanced formalism for knowledge representation and reasoning, which is very expressive in a precise mathematical sense: it allows one to express <i>every</i> property of finite structures that is decidable in the complexity class Σ<sup><i>P</i></sup><sub>2</sub> (NP<sup>NP</sup>). Thus, under widely believed… (More)

- Wolfgang Faber, Nicola Leone, Gerald Pfeifer
- JELIA
- 2004

The addition of aggregates has been one of the most relevant enhancements to the language of answer set programming (ASP). They strengthen the modeling power of ASP, in terms of concise problem representations. While many important problems can be encoded using nonrecursive aggregates, some relevant examples lend themselves for the use of recursive… (More)

- Wolfgang Faber, Gerald Pfeifer, Nicola Leone
- Artif. Intell.
- 2011

Users may access full items free of charge; copies of full text items generally can be reproduced, displayed or performed and given to third parties in any format or medium for personal research or study, educational or not-for-profit purposes without prior permission or charge, provided: • The authors, title and full bibliographic details is credited in… (More)

- Laks V. S. Lakshmanan, Nicola Leone, Robert B. Ross, V. S. Subrahmanian
- ACM Trans. Database Syst.
- 1997

Probability theory is mathematically the best understood paradigm for modeling and manipulating uncertain information. Probabilities of complex events can be computed from those of basic events on which they depend, using any of a number of strategies. Which strategy is appropriate depends very much on the known interdependencies among the events… (More)

- Georg Gottlob, Nicola Leone, Francesco Scarcello
- IJCAI
- 1999

We compare tractable classes of constraint satisfaction problems (CSPs). We first give a uniform presentation of the major structural CSP decomposition methods. We then introduce a new class of tractable CSPs based on the concept of hypertree decomposition recently developed in Database Theory. We introduce a framework for comparing paramet-ric… (More)

- Nicola Leone, Pasquale Rullo, Francesco Scarcello
- Inf. Comput.
- 1997

Disjunctive logic programs have become a powerful tool in knowledge representation and commonsense reasoning. This paper focuses on stable model semantics, currently the most widely acknowledged semantics for disjunctive logic programs. After presenting a new notion of unfounded sets for disjunctive logic programs, we provide two declarative… (More)

- Georg Gottlob, Nicola Leone, Francesco Scarcello
- FOCS
- 1998

This paper deals with the evaluation of acyclic Booleanconjunctive queries in relational databases. By well-known resultsof Yannakakis[1981], this problem is solvable in polynomial time;its precise complexity, however, has not been pinpointed so far. Weshow that the problem of evaluating acyclic Boolean conjunctivequeries is complete for LOGCFL, the class… (More)

dlv is a knowledge representation system, based on disjunctive logic programming, which ooers front-ends to several advanced KR formalisms. The system has been developed since one year at the Technical University of Vienna in an ongoing project funded by the Austrian Science Funds. After a report on the current state of the art in the implementation of dlv… (More)

- Georg Gottlob, Nicola Leone, Francesco Scarcello
- J. Comput. Syst. Sci.
- 1999

Several important decision problems on conjunctive queries (CQs) are NP-complete in general but become tractable, and actually highly parallelizable, if restricted to acyclic or nearly acyclic queries. Examples are the evaluation of Boolean CQs and query containment. These problems were shown tractable for conjunctive queries of bounded treewidth [9], and… (More)

Disjunctive Deductive Databases (DDDBs) | function-free disjunctive logic programs with negation in rule bodies allowed | have been recently recognized as a powerful tool for knowledge representation and commonsense reasoning. Much research has been spent on issues like semantics and complexity of DDDBs, but the important area of implementing DDDBs has been… (More)