Executing Suspended Logic Programs

Cybernetics and Systems Analysis, 1993

Journal of Automated Reasoning, 1994

In this paper, we study a new semantics of logic programming and deductive databases. Thepossible model semantics is introduced as a declarative semantics of disjunctive logic programs. The possible model semantics is an alternative theoretical framework to the classical minimal model semantics and provides a flexible inference mechanism for inferring negation in disjunctive logic programs. We also present a proof procedure for the possible model semantics and show that the possible model semantics has an advantage from the computational complexity point of view.

Annals of Mathematics and …, 1997

An operation for restricting deductive databases represented as logic programs is introduced. The constraints are coded in a separate database, and the operator puts the two databases together in order to provide a restricted view of the original database. The operator is given a semantics in terms of the immediate consequence operator. Then a transformational implementation is given and its correctness is proved with respect to the abstract semantics. The approach is presented at rst for positive programs and it is then extended to take negation as failure into account.

Lecture Notes in Computer Science, 1998

dlv is a deductive database system, based on disjunctive logic programming, which offers front-ends to several advanced KR formalisms. The system has been developed since the end of 1996 at Technische Universität Wien in an ongoing project funded by the Austrian Science Funds (FWF). Recent comparisons have shown that dlv is nowadays a state-of-the-art implementation of disjunctive logic programming. A major strength of dlv are its advanced knowledge modelling features. Its kernel language extends disjunctive logic programming by strong negation ( a la Gelfond and Lifschitz) and integrity constraints; furthermore, front-ends for the database language SQL3 and for diagnostic reasoning are available. Suitable interfaces allow dlv users to utilize base relations which are stored in external commercial database systems. This paper provides an overview of the dlv system and describes recent advances in its implementation. In particular, the recent implementation of incremental techniques for program evaluation, as well as the use of relational join optimization strategies appear particularly relevant for deductive database applications. These techniques are suitably extended in dlv for the efficient instantiation of nonmonotonic programs. Benchmarks on problems from different domains are also reported to give a feeling of the current system performance.

Lecture Notes in Computer Science, 1991

This paper relates our experience in integrating constraint resolution into an object-oriented deductive system. We motivate this work by showing that disjunctive information and global constraints fit naturally in an object-oriented model and are actually necessary to perform common tasks. We identify three difficulties in developing such an extended object-oriented system (namely, compilation, domain reduction, and heuristics) and propose a solution for each. We provide a formal semantics and prove the correctness of those three techniques. We illustrate the performance results with the implementation we have built in LAURE.

Future Databases '92, 1992

There are many ways in which the query answering process for deductive databases may be optimised. At the heart of many of these methods is some form of constraint on the variables of the query, so that facts which are not relevant to the query are not computed. In this paper we show how fold/unfold transformations may be used to propagate some forms of constraint which are not captured by techniques such as magic sets. In particular, the fold/unfold transformation provides a straightforward way to propagate constraints involving multiple occurrence of a variable.

Logic programming and …, 1995

An operation for restricting deductive databases represented as logic programs is introduced. The restrictions are represented in a separate deductive database. The operation is given an abstract semantics in terms of the immediate consequence operator. A transformational implementation is given and its correctness is proved with respect to the abstract semantics.

2013

SQL technology has evolved during last years, and systems are being more powerful and scalable. However, there exist yet some expressiveness limitations that can be otherwise overcome with inputs from deductive databases. This paper focuses on both practical and theoretical expressiveness issues in current SQL implementations that are overcome in the Datalog Educational System (DES), a deductive system which also includes extended SQL queries with respect to the SQL standard and current DBMS’s. Also, as external database access and interoperability are allowed in DES, results from the deductive field can be tested on current DBMS’s. For instance: Less-limited SQL formulations as non-linear recursive queries, novel features as hypothetical queries, and other query languages as Datalog and Extended Relational Algebra. In addition, some notes on performance are taken.

2019 IEEE Second International Conference on Artificial Intelligence and Knowledge Engineering (AIKE), 2019

Database Reformulation is the process of rewriting the data and rules in deductive databases in a functionally equivalent manner, ideally in ways that decrease query processing time while keeping storage costs within acceptable bounds. Early research in this area focussed on materializing existing views, i.e. caching those views as data. Subsequent research investigated the problem of inventing new views to afford different opportunities for materialization. The Bounding Theorem, introduced in this latter effort, is significant in that it gives a finite bound on the number of useful reformulations for conjunctive queries. Unfortunately, the number of possibilities allowed by the Bounding Theorem is doubly exponential in the size of the query (not the database instance). In this paper, we show that we can reduce that double exponential to a single exponential. We first present an improved version of the Bounding Theorem, called the Subgoal Theorem. We then present an additional resul...

Proceedings of the eighth ACM SIGACT-SIGMOD-SIGART symposium on Principles of database systems - PODS '89

The features of logic programming that seem unconventional from the viewpoint of classical logic can be explained in terms of constructivistic logic. We motivate and propose a constructivistic proof theory of non-Horn logic programming. Then, we apply this formalization for establishing results of practical interest. First, we show that 'stratification can be motivated in a simple and intuitive way. Relying on similar motivations, we introduce the larger classes of 'loosely stratified' and 'constructively consistent' programs. Second, we give a formal basis for introducing quantifiers into queries and logic programs by defining 'constructively domain independent' formulas. Third, we extend the Generalized Magic Sets procedure to loosely stratified and constructively consistent programs, by relying on a 'conditional f^ucpoint' procedure.