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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)

- 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
- 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)

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

The addition of aggregates has been one of the most relevant enhancements to the language of answer set programming (ASP). They strengthen the modelling power of ASP in terms of natural and concise problem representations. Previous semantic definitions typically agree in the case of nonrecursive aggregates, but the picture is less clear for aggregates… (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 parametric… (More)

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

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)

- Thomas Eiter, Georg Gottlob, Nicola Leone
- Theor. Comput. Sci.
- 1997

Abduction ~ from observations and a theory, find using hypotheses an explanation for the observations gained increasing interest during the last years. This form of reasoning has wide applicability in different areas of computer science; in particular, it has been recognized as an important principle of common-sense reasoning. In this paper, we define a… (More)

- Thomas Eiter, Wolfgang Faber, Nicola Leone, Gerald Pfeifer, Axel Polleres
- Artif. Intell.
- 2003

We propose a new declarative planning language, called K, which is based on principles and methods of logic programming. In this language, transitions between states of knowledge can be described, rather than transitions between completely described states of the world, which makes the language well-suited for planning under incomplete knowledge.… (More)