. A constraint satisfaction problem involves finding values for variables subject to constraints on which combinations of values are allowed. In some cases it may be impossible or impractical to solve these problems completely. We may seek to partially solve the problem, in particular by satisfying a maximal number of constraints. Standard backtracking and local consistency techniques for solving constraint satisfaction problems can be adapted to cope with, and take advantage of, the differences between partial and complete constraint satisfaction. Extensive experimentation on maximal satisfaction problems illuminates the relative and absolute effectiveness of these methods. A general model of partial constraint satisfaction is proposed. 1 Introduction Constraint satisfaction involves finding values for problem variables subject to constraints on acceptable combinations of values. Constraint satisfaction has wide application in artificial intelligence, in areas ranging from temporal r...

problem (csp), namely, naive backtracking (BT), backjumping (BJ), conflict-directed backjumping

Conjunctive-query containment is recognized as a fundamental problem in database query evaluation and optimization. At the same time, constraint satisfaction is recognized as a fundamental problem in artificial intelligence. What do conjunctive-query containment and constraint satisfaction have in common? Our main conceptual contribution in this paper is to point out that, despite their very different formulation, conjunctive-query containment and constraint satisfaction are essentially the same problem. The reason is that they can be recast as the following fundamental algebraic problem: given two finite relational structures A and B, is there a homomorphism h : A ! B? As formulated above, the homomorphism problem is uniform in the sense that both relational structures A and B are part of the input. By fixing the structure B, one obtains the following non-uniform problem: given a finite relational structure A, is there a homomorphism h : A ! B? In general, non-uniform tractability results do not uniformize. Thus, it is natural to ask: which tractable cases of non-uniform tractability results for constraint satisfaction and conjunctive-query containment do uniformize? Our main technical contribution in this paper is to show that several cases of tractable non-uniform constraint satisfaction problems do indeed uniformize. We exhibit three non-uniform tractability results that uniformize and, thus, give rise to polynomial-time solvable cases of constraint satisfaction and conjunctive-query containment.

In this paper the issue of soft constraint satisfaction is discussed from a fuzzy set theoretical point of view. A fuzzy constraint is considered as a fuzzy relation. Different possible definitions for the degree of joint satisfaction of a set of fuzzy constraints are given, covering specific other soft constraint satisfaction problem (CSP) types such a partial and hierarchical CSP. It is shown that the classical CSP solving heuristics based on variable and value evaluations can be generalised and used to guide the solution construction process for solving fuzzy CSPs, and that the heuristic search can be replaced by branch-and-bound search. The solution process is illustrated with an example from the CSP literature. Finally, research issues are discussed. 1. Introduction In the recent years there has been a growing interest in soft constraint satisfaction. In general, in a soft CSP not all the given constraints need to be satisfied --- either because all of them cannot be met, theoret...

We propose a model-based approach to automated 3D extraction of buildings from aerial images. We focus on a reconstruction strategy that is not restricted to a small class of buildings. Therefore, we employ a generic modeling approach which relies on the well dened combination of building part models. Building parts are classied by their roof type.

Enforcing local consistencies is one of the main features of constraint reasoning. Which level of local consistency should be used when searching for solutions in a constraint network is a basic question. Arc consistency and partial forms of arc consistency have been widely studied, and have been known for sometime through the forward checking or the MAC search algorithms. Until recently, stronger forms of local consistency remained limited to those that change the structure of the constraint graph, and thus, could not be used in practice, especially on large networks. This paper focuses on the local consistencies that are stronger than arc consistency, without changing the structure of the network, i.e., only removing inconsistent values from the domains. In the last five years, several such local consistencies have been proposed by us or by others. We make an overview of all of them, and highlight some relations between them. We compare them both theoretically and experimentally, considering their pruning efficiency and the time required to enforce them.

There have been some straightforward efforts to extend Allen's interval-based temporal logic to spatial dimensions by using Cartesian tuples of relations [6]. We take a different approach based on a study of the kind of information that best relates two entities in 2-dimensional space qualitatively. The relevant spatial categories turn out to be "projection" and "orientation". We define a small set of spatial relations and stress the importance of making their reference frames explicit. Furthermore, we introduce "abstract maps", an analogical representation that inherently reflects the structure of the represented domain, and demonstrate their use in spatial reasoning. This scheme also facilitates "coarse" reasoning and the hierarchical organization of knowledge. These representational issues form the basis for an experimental system to develop "cognitive maps" from 2-D scanned layout plans of buildings. 1 Introduction Cognitive spatial concepts are qualitative in nature. Despite the ...

. Increasing interest for configuration similarity is currently developing in the context of Digital Libraries, Spatial Databases and Geographical Information Systems. The corresponding queries retrieve all database configurations that match an input description (e.g., "find all configurations where an object x 0 is about 5km northeast of another x 1 , which, in turn, is inside object x 2 "). This paper introduces a framework for configuration similarity that takes into account all major types of spatial constraints (topological, direction, distance). We define appropriate fuzzy similarity measures for each type of constraint to provide flexibility and allow the system to capture real-life needs. Then we apply pre-processing techniques to explicate constraints in the query, and present algorithms that effectively solve the problem. Extensive experimental results demonstrate the applicability of our approach to images and queries of considerable size. 1. INTRODUCTION As opposed to visu...

We present an approach to the parsing of dependency structures which. brings together the notion of parsing as candidate elimination, the use of graded constraints, and the parallel disambiguation of related structural representations. The approach aims at an increased level of robustness by accepting constraint violations in a controlled way, combining redundant and possibly conflicting information on different represenrational levels, and facilitating partial parsing as a natural mode of behavior.

A large class of problems in AI and other areas of computer science can be viewed as constraint-satisfaction problems. This includes problems in machine vision, belief maintenance, scheduling, temporal reasoning, type reconstruction, graph theory, and satisability. In general, the constraint satisfaction-problem is NP-complete, so searching for tractable cases is an active research area. It turns out that constraint satisfaction has an intimate connection with database theory: constraint-satisfaction problems can be recast as database problems and database problems can be recast as constraint-satisfaction problems. In this tutorial, I will cover the fundamentals of constraints saisfaction and describe its intimate relationship with database theory from various perspectives. 1 Introduction Since the early 1970s, researchers in articial intelligence have investigated a class of combinatorial problems that became known as constraint-satisfaction problems (CSP). The input to such a pro...