Local consistency techniques have been introduced in logic programming in order to extend the application domain of logic programming languages. The existing languages based on these techniques consider arithmetic constraints applied to variables ranging over nite integer domains. This makes difficult a natural and concise modelling as well as an efficient solving of a class of NP-complete combinatorial search problems dealing with sets. To overcome these problems, we propose a solution which consists in extending the notion of integer domains to that of set domains (sets of sets). We specify a set domain by an interval whose lower and upper bounds are known sets, ordered by set inclusion. We define the formal and practical framework of a new constraint logic programming language over set domains, called Conjunto. Conjunto comprises the usual set operation symbols ([ � \ � n), and the set inclusion relation (). Set expressions built using the operation symbols are interpreted as relations (s [ s1 = s2,...). In addition, Conjunto provides us with a set of constraints called graduated constraints (e.g. the set cardinality) which map sets onto arithmetic terms. This allows us to handle optimization problems by applying a cost function to the quantifiable, i.e., arithmetic, terms which are associated to set terms. The constraint solving in Conjunto is based on local consistency techniques using interval reasoning which are extended to handle set constraints. The main contribution of this paper concerns the formal definition of the language and its design and implementation as a practical language.

The paper compares two popular strategies for solving propositional satisfiability, backtracking search and resolution, and analyzes the complexity of a directional resolution algorithm (DR) as a function of the "width" (w) of the problem's graph.

work in the ESPRIT project DiSCiPl. The project aims at devising advanced tools for debugging of constraint logic programs. Acentral problem in program development is obtaining a program which satis es the user's expectations. When considering a given program, a natural question is then whether or not it

The performance of backtracking algorithms for solving finite-domain constraint satisfaction problems can be improved substantially by look-back and look-ahead methods. Look-back techniques extract information by analyzing failing search paths that are terminated by dead-ends. Look-ahead techniques use constraint propagation algorithms to avoid such dead-ends altogether. This survey describes a number of look-back variants including backjumping and constraint recording which recognize and avoid some unnecessary explorations of the search space. The last portion of the paper gives an overview of look-ahead methods such as forward checking and dynamic variable ordering, and discusses their combination with backjumping.

This paper discusses the algorithm we are using for the mediation of queries to disparate information sources in a Context Interchange system, where information sources may have di erent interpretations arising from their respective context. Queries are assumed to be formulated without regard for semantic heterogeneity, and are rewritten to corresponding mediated queries by taking into account the semantics of data codi ed in axioms associated with sources and receivers (the corresponding context theories). Our approach draws upon recent advances in abductive logic programming and presents an integration of techniques for query rewriting and semantic query optimization. We also demonstrate how thiscanbe e ciently implemented using the constraint logic programming system ECLiPSe. 1

Abstract. Web site semantic content veri cation can be a tedious and error prone task. In this paper we propose a framework for syntactic validation and semantic veri cation based on the logic programming language XCentric. The high declarative model of this language based on a new uni cation algorithm along with an interface to semistructured data provides an elegant framework for semantic error detection. The result is an easy to follow model to improve website quality and management. 1

This paper describes a proposal to incorporate finite domain constraints in a functional logic system. The proposal integrates functions, higher-order patterns, partial applications, non-determinism, logical variables, currying, types, lazyness, domain variables, constraints and finite domain propagators.

We propose a new indexed-category syntax and semantics of Weak Hereditarily Harrop logic programming with constraints, based on resolution over tau-categories:finite product categories with canonical structure.

Abstract. Local consistency techniques have beenintroduced in logic programming in order to extend the application domain of logic programming languages. The existing languages based on these techniques consider arithmetic constraints applied to variables ranging over nite integer domains. This makes di cult a natural and concise modelling as well as an e cient solving of a class of NP-complete combinatorial search problems dealing with sets. To overcome these problems, we propose a solution which consists in extending the notion of integer domains to that of set domains (sets of sets). We specify a set domain by aninterval whose lower and upper bounds are known sets, ordered by set inclusion. We de ne the formal and practical framework of a new constraint logic programming language over set domains, called Conjunto. Conjunto comprises the usual set operation symbols ([ � \ � n), and the set inclusion relation (). Set expressions built using the operation symbols are interpreted as relations (s [ s1 = s2,...). In addition, Conjunto provides us with a set of constraints called graduated constraints (e.g. the set cardinality) which map sets onto arithmetic terms. This allows us to handle optimization problems by applyinga cost function to the quanti able, i.e., arithmetic, terms which are associated to set terms. The constraint solving in Conjunto is based on local consistency techniques using interval reasoning which are extended to handle set constraints. The main contribution of this paper concerns the formal de nition of the language and its design and implementation as a practical language.

: The placement of rectangular objects without overlapping on a bounded surface is a generic problem that may have many applications. Space planning, chipset placement, cutting-stock problems, point-feature label placement, or the placement of articles on a newspaper page, are all instances of this more abstract problem. All these applications are concerned with the insertion of rectangular objects on a part of a bounded free surface. It is therefore important to be able to efficiently model the free space of the bounded surface. In this article we present a method to compute free space. The method is based on an iterative insertion process. Our algorithm neither depends on the size of the object to insert, nor on the method of placement. The first feature improves efficiency, while the second allows us to compare different placement methods, and to parameterize the placement system using resolution heuristics. Key Words: Placement, algorithms, free space Category: I.3, I.3.5, I.3.6,...