In the recent years, constraint programming has been applied to a wide variety of academic and industrial non-preemptive scheduling problems, i.e., problems in which activities cannot be interrupted. In comparison, pr...
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In the recent years, constraint programming has been applied to a wide variety of academic and industrial non-preemptive scheduling problems, i.e., problems in which activities cannot be interrupted. In comparison, preemptive scheduling problems have received almost no attention from both the Operations Research and the Artificial Intelligence community. Motivated by the needs of a specific application, we engaged in a study of the applicability of constraint programming techniques to preemptive scheduling problems. This paper presents the algorithms we developed and the results we obtained on the preemptive variant of the famous "job-shop scheduling problem." Ten heuristic search strategies, combined with two different constraint propagation techniques, are presented, and compared using two well-known series of job-shop scheduling instances from the literature. The best combination, which relies on "limited discrepancy search" and on "edge-finding" techniques, is shown to provide excellent solutions to the preemptive job-shop scheduling problem. A mean relative distance to the optimal solution of 0.32% is achieved in five minutes, on instances with 10 jobs and 10 machines (100 activities).
The filtering method considered in this paper is based on approximation of a spatial object in d-dimensional space by the minimal convex polyhedron that encloses the object and whose facets are normal to preselected a...
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The filtering method considered in this paper is based on approximation of a spatial object in d-dimensional space by the minimal convex polyhedron that encloses the object and whose facets are normal to preselected axes. These axes are not necessarily the standard coordinate axes;furthermore, their number is not determined by the dimension of the space. We optimize filtering by selecting optimal such axes based on a preprocessing analysis of stored objects or a sample thereof. The number of axes selected represents a trade-off between access time and storage overhead, as more axes usually lead to better filtering but require more overhead to store the associated access structures. We address the problem of minimizing the number of axes required to achieve a predefined quality of filtering and the reverse problem of optimizing the quality of filtering when the number of axes is fixed. In both cases we also show how to find an optimal collection of axes. To solve these problems, we introduce and study the key notion of separability classification, which is a general tool potentially useful in many applications of a computational geometry flavor. The approach is best suited to applications in which the spatial data is relatively static, some directions are more dominant than others, and the dimension of the space is not high;maps are a prime example.
In this paper we advocate for more flexible and user-friendly constraint solving environments, as well as for constraint programming languages which have great expressive power while maintaining a formal semantics bas...
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In this paper we advocate for more flexible and user-friendly constraint solving environments, as well as for constraint programming languages which have great expressive power while maintaining a formal semantics based on few crucial concepts. We cite some of our work in these directions and we hint at subjects of our future research.
constraint retraction can be described, in general, as the possibility of deleting a previously stated piece of information. This is obviously very convenient in many programming frameworks, especially in those that i...
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constraint retraction can be described, in general, as the possibility of deleting a previously stated piece of information. This is obviously very convenient in many programming frameworks, especially in those that involve some level of interaction between the user and the system, or also in those concerning rescheduling or replanning. Nevertheless, constraint retraction is usually not provided in current constraint programming environments. This is mainly due to its high complexity and also to its non-monotonic nature, which would make most of such systems much more complex to reason with. In this paper we avoid these problems by considering a specific constraint programming framework, called clp (FD), that is, constraint logic programming (CLP) over finite domain (FD) constraints. We propose an algorithm which deletes a constraint from a set of FD constraints, while maintaining partial arc-consistency, which is usual in this programming framework. What is crucial is that the retraction operation we propose is incremental, in that it follows the chain of dependencies among variables which are set by the nature of the FD constraints, and by doing so it updates only the part of the constraint set which is affected by the deletion. We also detail how constraint retraction can be incorporated in the FD constraint solver and we evaluate its behavior within the clp (FD) system. Experimental results on usual benchmarks, on classes of problems of increasing connectivity, and also on a real-life problem show that in almost all cases the use of our retraction algorithm provides great speed-up with respect to standard methods while not slowing down the clp (FD) system when no retraction is performed. This provides the system with an efficient way of retracting constraints while not changing its performance when the user does not want to use this new feature.
In computational linguistics, we are often interested in developing grammar formalisms declaratively. However, tractability often becomes a problem then. Therefore, we want to argue for the use of constraint logic pro...
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We show that constraint Logic programming (CLP) can serve as a conceptual basis and as a practical implementation platform for the model checking of infinite-state systems. Our contributions are: (1) a semantics-prese...
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ISBN:
(纸本)3540657037
We show that constraint Logic programming (CLP) can serve as a conceptual basis and as a practical implementation platform for the model checking of infinite-state systems. Our contributions are: (1) a semantics-preserving translation of concurrent systems into CLP programs, (2) a method for verifying safety and liveness properties on the CLP programs produced by the translation. We have implemented the method in a CLP system and verified well-known examples of infinite-state programs over integers, using here linear constraints as opposed to Presburger arithmetic as in previous solutions.
Experience using constraint programming to solve real-life problems has shown that finding an efficient solution to the problem often requires experimentation with different constraint solvers or even building a probl...
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constraint programming is an emerging technology that offers an original approach allowing for efficient and flexible solving of complex problems. Its main advantage relies in its ability to compute with partial infor...
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ISBN:
(纸本)9780769504155
constraint programming is an emerging technology that offers an original approach allowing for efficient and flexible solving of complex problems. Its main advantage relies in its ability to compute with partial information expressed in terms of *** constraints are monotonically accumulated during the program execution in order to restrict the problem search space. In this paper we address one of the cornerstones of this technology, namely the current lack of debugging facilities. In particular, visualization and understanding of the underlying constraint system during program executions is very important. We propose to structure this huge, flat and intricate part of the execution data in order to provide access to high level examination of its evolution. More precisely, we present a means to hierarchically organize sets of constraints in order to divide them into manageable parts while preserving computation correctness. Soundness of our method is shown, an algorithm supporting it is given, and an implemented prototype exhibiting its effectiveness is described.
This paper exploits the point of view of constraint programming as computation in a logical system, namely constraint logic We define the basic ingredients of constraint logic, such as constraint models and generalise...
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ISBN:
(纸本)3540616292
This paper exploits the point of view of constraint programming as computation in a logical system, namely constraint logic We define the basic ingredients of constraint logic, such as constraint models and generalised polynomials. We show that constraint logic is an institution, and we internalise the study of constraint logic to the framework of category-based equational logic. By showing that constraint logic is a special case of category-based equational logic, we integrate the constraint logic programming paradigm into equational logic programming. Results include a Herbrand theorem for constraint logic programming characterising Herbrand models as initial models in constraint logic.
We show how to implement efficient records in constraint logic programming (CLP) and its generalization concurrent constraint programming (CCP). Records can be naturally integrated into CCP as a new constraint domain....
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