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Resultados de búsqueda para Constraint Logic Programming

Static Performance Guarantees for Programs with Run-time Checks

Instrumenting programs for performing runtime checking of properties, such as regular shapes, is a common and useful technique that helps programmers detect incorrect program behaviors. This is especially true in dynamic languages such as Prolog. However, such runtime checks inevitably introduce runtime overhead (in execution time, memory, energy, etc.). Several approaches have been proposed for reducing this overhead, such as eliminating the checks that can statically be proved to always succeed, and/or optimizing the way in which the (remaining) checks are performed. However, there are cases in which it is not possible to remove all checks statically (e.g., open libraries which must check their interfaces, complex properties, unknown code, etc.) and in which, even after optimizations, these remaining checks may still introduce an unacceptable level of overhead. It is thus important for programmers to be able to determine the additional cost due to the runtime checks and compare it to some notion of admissible cost. The common practice used for estimating runtime checking overhead is profiling, which is not exhaustive by nature. Instead, we propose a method that uses static analysis to estimate such overhead, with the advantage that the estimations are functions parameterized by input data sizes. Unlike profiling, this approach can provide guarantees for all possible execution traces, and allows assessing how the overhead grows as the size of the input grows. Our method also extends an existing assertion verification framework to express «admissible» overheads, and statically and automatically checks whether the instrumented program conforms with such specifications. Finally, we present an experimental evaluation of our approach that suggests that our method is feasible and promising.

Autores: Maximiliano Klemen / Nataliia Stulova / Pedro Lopez-Garcia / Manuel V. Hermenegildo / José Morales / 
Palabras Clave: abstract interpretation - Assertions - Constraint Logic Programming - Program analysis - Resource Usage Analysis - Run-time Checks

Semantic Analysis of SQL Statements in DES (Trabajo en progreso)

This paper presents an on-going work that includes semantic analysis of SQL statements in the database system DES. Following Brass&Goldberg, SQL statements, while syntactically correct, can exhibit symptoms of bad design. By warning users about such symptoms, both the learning curve of students as well as productivity of SQL practitioners can be enhanced. Some errors include inconsistent conditions, lack of correlations in joins, unused tuple variables and the like. Here, we describe the semantic checker developed for DES, which applies several techniques. In particular, it applies abstraction with CLP solving, and specific algorithms for the different kind of errors. This proposal has been implemented in the deductive system DES and available at des.sourceforge.net.

Autores: Fernando Sáenz Pérez / 
Palabras Clave: Constraint Logic Programming - Datalog - Semantic Analysis - SQL

A General Implementation Framework for Tabled CLP

This is a summary of [PCHS12], where a framework to combine tabling evaluation [TS86, War92] and constraint logic programming [JM94] is described (TCLP). This combination has been studied previously from a theoretical point of view [Tom97, Cod95], where it is shown that the constraint domain needs to offer projection and entailment checking operations in order to ensure completeness w.r.t. the declarative semantics. However, existing TCLP frameworks and implementations lack a complete treatment of constraint projection and / or entailment. The novelty of our proposal is that we present a complete implementation framework for TCLP, independent from the constraint solver, which can use either precise or approximate projection and entailment, possibly with optimizations.

Autores: Pablo Chico de Guzmán / Manuel Carro / Manuel V. Hermenegildo / Peter Stuckey / 
Palabras Clave: Constraint Logic Programming - Implementation - Performance - Tabling

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