Enrico Pontelli

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In this paper we present a novel execution model for parallel implementation of logic programs which is capable of exploiting both independent and-parallelism and or-parallelism in an efficient way. This model extends the stack copying approach, which has been successfully applied in the Muse system to implement or-parallelism, by integrating it with proven(More)
In this paper, we present two alternative approaches to defining answer sets for logic programs with arbitrary types of abstract constraint atoms (c-atoms). These approaches generalize the fixpoint-based and the level mapping based answer set semantics of normal logic programs to the case of logic programs with arbitrary types of c-atoms. The results are(More)
This technical note describes a monotone and continuous fixpoint operator to compute the answer sets of programs with aggregates. The fixpoint operator relies on the notion of aggregate solution. Under certain conditions, this operator behaves identically to the three-valued immediate consequence operator Φ P for aggregate programs, independently proposed(More)
We provide a new perspective on the semantics of logic programs with arbitrary abstract constraints. To this end, we introduce several notions of computation. We use the results of computations to specify answer sets of programs with constraints. We present the rationale behind the classes of computations we consider, and discuss the relationships among(More)
An extended logic programming language is presented, that embodies the fundamental form of set designation based on the (nesting) element insertion operator. The kind of sets to be handled is characterized both by adaptation of a suitable Herbrand universe and via axioms. Predicates 2 and = designating set membership and equality are included in the base(More)
In recent years we have witnessed a rapid development of logical systems— non-monotonic logics—that provide the ability to retract existing theorems via introduction of new axioms. In the context of logic programming, non-monotonic behavior has been accomplished by allowing the use of negation in the body of clauses. The presence of negation leads to a(More)
Since the early days of logic programming, researchers in the field realized the potential for exploitation of parallelism present in the execution of logic programs. Their high-level nature, the presence of nondeterminism, and their referential transparency, among other characteristics, make logic programs interesting candidates for obtaining speedups(More)
This paper presents a novel methodology to analyze low resolution (e.g., 6A to 10A) protein density map, that can be obtained through electron cryomicroscopy. At such resolutions, it is often not possible to recognize the backbone chain of the protein, but it is possible to identify individual structural elements (e.g., alpha-helices and beta-sheets). The(More)