Results 1 
7 of
7
Abduction in Logic Programming
"... Abduction in Logic Programming started in the late 80s, early 90s, in an attempt to extend logic programming into a framework suitable for a variety of problems in Artificial Intelligence and other areas of Computer Science. This paper aims to chart out the main developments of the field over th ..."
Abstract

Cited by 538 (74 self)
 Add to MetaCart
Abduction in Logic Programming started in the late 80s, early 90s, in an attempt to extend logic programming into a framework suitable for a variety of problems in Artificial Intelligence and other areas of Computer Science. This paper aims to chart out the main developments of the field over the last ten years and to take a critical view of these developments from several perspectives: logical, epistemological, computational and suitability to application. The paper attempts to expose some of the challenges and prospects for the further development of the field.
SSemantics Approach: Theory and Applications
, 1994
"... The paper is a general overview of an approach to the semantics of logic programs whose aim is finding notions of models which really capture the operational semantics, and are therefore useful for defining program equivalences and for semanticsbased program analysis. The approach leads to the intr ..."
Abstract

Cited by 115 (26 self)
 Add to MetaCart
The paper is a general overview of an approach to the semantics of logic programs whose aim is finding notions of models which really capture the operational semantics, and are therefore useful for defining program equivalences and for semanticsbased program analysis. The approach leads to the introduction of extended interpretations which are more expressive than Herbrand interpretations. The semantics in terms of extended interpretations can be obtained as a result of both an operational (topdown) and a fixpoint (bottomup) construction. It can also be characterized from the modeltheoretic viewpoint, by defining a set of extended models which contains standard Herbrand models. We discuss the original construction modeling computed answer substitutions, its compositional version and various semantics modeling more concrete observables. We then show how the approach can be applied to several extensions of positive logic programs. We finally consider some applications, mainly in the area of semanticsbased program transformation and analysis.
D'ej`a vu in fixpoints of logic programs
 in Proceedings of the North American Conference on Logic Programming
, 1989
"... We investigate properties of logic programs that permit refinements in their fixpoint evaluation and shed light on the choice of control strategy. A fundamental aspect of a bottomup computation is that we must constantly check to see if the fixpoint has been reached. If the computation iteratively ..."
Abstract

Cited by 26 (5 self)
 Add to MetaCart
We investigate properties of logic programs that permit refinements in their fixpoint evaluation and shed light on the choice of control strategy. A fundamental aspect of a bottomup computation is that we must constantly check to see if the fixpoint has been reached. If the computation iteratively applies all rules, bottomup, until the fixpoint is reached, this amounts to checking if any new facts were produced after each iteration. Such a check also enhances efficiency in that duplicate facts need not be reused in subsequent iterations, if we use the Seminaive fixpoint evaluation strategy. However, the cost of this check is a significant component of the cost of bottomup fixpoint evaluation, and for many programs the full check is unnecessary. We identify properties of programs that enable us to infer that a much simpler check (namely, whether any fact was produced in the previous iteration) suffices. While it is in general undecidable whether a given program has these properties, we develop techniques to test sufficient conditions, and we illustrate these techniques on some simple programs that have these properties. The significance of our results lies in the significantly larger class of programs for which bottomup evaluation methods, enhanced with the optimizations that we propose, become competitive with standard (topdown) implementations of logic programs. This increased efficiency is achieved without compromising the completeness of the bottomup approach; this is in contrast to the incompleteness that accompanies the depthfirst search strategy that is central to most topdown implementations.
Separating concurrent languages with categories of language embeddings
 In Proceedings of the 23 rd Annual ACM Symposium on Theory of Computing
, 1991
"... Concurrent programming enjoys a proliferation of languages but suffers from the lack of a general method of language comparison. In particular, concurrent (as well as sequential) programming languages cannot be usefully distinguished based on complexitytheoretic considerations, since most of them ..."
Abstract

Cited by 12 (1 self)
 Add to MetaCart
Concurrent programming enjoys a proliferation of languages but suffers from the lack of a general method of language comparison. In particular, concurrent (as well as sequential) programming languages cannot be usefully distinguished based on complexitytheoretic considerations, since most of them are Turingcomplete. Nevertheless, differences between programming languages matter, else we would not have invented so many of them. We develop a general method for comparing concurrent programming languages based on their algebraic (structural) complexity, and, using this method, achieve separation results among many wellknown concurrent languages. The method is not restricted to concurrent languages. It can be used to compare the algebraic complexity of abstract machine models, other families of programming languages, logics, and, more generaly, any family of languages with some syntactic operations and a notion of semantic equivalence. The method can also be used to compare the algebraic complexity of families of operations wit hin a language or across languages. We note that using the method we were able to compare languages and computational models that do not have a common semantic basis.
Modular Logic Programs over Finite Domains
 PROC. EIGHT ITALIAN CONFERENCE ON LOGIC PROGRAMMING
, 1993
"... In this paper we study the properties of a compositional semantics for logic programs and its applications to modular analysis and logicbased databases, focusing on programs defined on a finite domain (i.e. on a function free finite signature). By this restriction we obtain a finite characterizatio ..."
Abstract

Cited by 11 (6 self)
 Add to MetaCart
In this paper we study the properties of a compositional semantics for logic programs and its applications to modular analysis and logicbased databases, focusing on programs defined on a finite domain (i.e. on a function free finite signature). By this restriction we obtain a finite characterization of the compositional semantics which has the same correctness and compositionality properties of the original (fixpointbased) definition, even if the latter could introduce infinite denotations also for finite domains programs. This property is particularly suitable for semanticsbased program analysis, since it allows to identify a class of abstract domains for which the same finite characterization of the (abstract) compositional semantics holds. By combining this result with an existing framework for the modular analysis of logic programs, we can obtain a compositional analysis without requiring an additional level of abstraction. The finiteness of our characterization can also be usef...
Observable Behaviors and Equivalences of Logic Programs
 Information and Computation
, 1992
"... We first introduce a general semantic scheme for logic programs which provides a uniform framework for defining different compositional semantics parametrically wrt a given notion of observability. The equivalence of the operational (topdown) and fixpoint (bottomup) construction of the semantics i ..."
Abstract

Cited by 10 (3 self)
 Add to MetaCart
We first introduce a general semantic scheme for logic programs which provides a uniform framework for defining different compositional semantics parametrically wrt a given notion of observability. The equivalence of the operational (topdown) and fixpoint (bottomup) construction of the semantics is ensured by the scheme (provided a congruence property is verified). We then define several observational equivalences on logic programs and investigate how they are related. The equivalences are based on various observables (successful derivations, computed answers, partial computed answers and call patterns) and on a notion of program composition. For each observational equivalence we study the relation with a suitable formal semantics, by investigating correctness and full abstraction properties. All the semantics we consider are obtained as instances of the general scheme. 1 Introduction According to [36], the semantics of positive logic programs is defined in modeltheoretic terms (th...
Institutions for Logic Programming
 Theoretical Computer Science
, 1997
"... The compositionality of the semantics of logic programs with respect to (different varieties of) program union has been studied recently by a number of researchers. The approaches used can be considered quite adhoc in the sense that they provide, from scratch, the semantic constructions needed to e ..."
Abstract

Cited by 4 (1 self)
 Add to MetaCart
The compositionality of the semantics of logic programs with respect to (different varieties of) program union has been studied recently by a number of researchers. The approaches used can be considered quite adhoc in the sense that they provide, from scratch, the semantic constructions needed to ensure compositionality and, in some cases, full abstraction in the given framework. In this paper, we study the application of general algebraic methods for obtaining, systematically, this kind of results. In particular, the method proposed consists in studying the adequate institution for describing the given class of logic programs and, then, in using general institutionindependent results to prove compositionality and full abstraction. This is done in detail for the class of definite logic programs with respect to three kinds of composition operations: Wunion, standard union and module composition. In addition two different institutions are considered: the standard institution...