The course timetable construction is a procedure that every academic department has to carry out at least twice annually, more times if some of the requirements change. These requirements indicate that a collection of...
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The course timetable construction is a procedure that every academic department has to carry out at least twice annually, more times if some of the requirements change. These requirements indicate that a collection of elements must be taken in mind in order for an acceptable solution to be found. They come either from the inherent constraints of the problem or from the involved parties, namely teachers and students. A requirement that is very difficult to statisfy is the one of optimality, which means that the constructed timetable should be the best among the legal ones, according to some quantified quality criteria. In this paper, a method for tackling the course timetable construction problem for academic departments is presented, which is based on constraint logic programming (CLP) for the early pruning of the search space and on the usage of intelligent heuristics in order to guide the search to the generation of nearly optimum solutions. A specific system is presented, named ACTS (Automated Course Timetabling System), which has been implemented in the ECL i PS e language. This system is currently in use by the Department of Informatics of the University of Athens for the purpose of aiding the semester course timetable construction.
Commodity exchanges provide potential market structures for electronic trading because commodity products have relatively simple and well-standardized product attributes. Most existing electronic trading systems are i...
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Commodity exchanges provide potential market structures for electronic trading because commodity products have relatively simple and well-standardized product attributes. Most existing electronic trading systems are introduced for financial exchanges, where qualities of traded products (such as stocks and bonds) are homogeneous, thus taking into account only bid and offer prices for computer-mediated order matching. However, a single commodity market, such as the cotton or grain market, is made up of many heterogeneous goods that are similar to each other but have different product qualities and contract terms. In addition to the price, commodity traders have other pertinent preference ranges over product attributes and delivery conditions. We delineate an electronic call market system for commodity trading, which optimizes the realization of traders' utilities over extended product attributes beyond the price. The electronic call market not only maximizes the total surplus of market participants based on bid and ask prices but also satisfies their qualitative preferences over other attributes, which are difficult to include in the qualitative prices. The trading mechanism of the electronic call market integrates an economic auction model with a social choice model to produce a Pareto-improved transaction. Market simulations are conducted to validate the performance of the proposed electronic call market. The order matching system of the electronic call market is implemented using constraint logic programming.
The authors of this paper have investigated the potential of using the recently developed constraint logic programming (CLP) languages as an implementation engine for qualitative simulation. This was initiated by the ...
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The authors of this paper have investigated the potential of using the recently developed constraint logic programming (CLP) languages as an implementation engine for qualitative simulation. This was initiated by the recognition that both utilize constraints as a basic representational formalism and constraint propagation as the inference mechanism. The focus of the work was on an advanced qualitative simulation system that uses fuzzy sets to describe the values of the system variables (FuSim). This led to a number of technical innovations that allows the semi-quantitative quantity space to be represented on a finite computational domain, and an incremental algorithm that makes active (constructive) use of the constraints rather than the passive use for consistency checking employed in conventional qualitative simulation algorithms. However, the approach described is applicable to any semi-quantitative simulation system. The system, called CLP-FuSim, is implemented in the CLP language CHIP and has been tested and validated on a number of benchmark examples. The resulting performance is as least as good as the Lisp counterpart;however, the CLP version has the distinct advantage of declarative semantics and non-determinism.
In this article we try to illustrate that constraint logic programming (CLP) systems allow easy expression and solution of constrained decision problems. In order to do so, this paper proposes CLP solutions for two in...
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In this article we try to illustrate that constraint logic programming (CLP) systems allow easy expression and solution of constrained decision problems. In order to do so, this paper proposes CLP solutions for two industrial linear optimization problems respectively using the Prolog III and the CHIP language. The first problem, a mixed linear multicriteria selection problem, illustrates the general linear rational solver. In order to fix some integer variables a branch and bound rounding heuristic is formulated. The second problem, a linear integer multicriteria location problem, is only concerned with integer finite domain variables and is particularly adapted to the CHIP system that provides a computation domain handling such variables.
The development of more powerful Concurrent constraint logic programming (CCLP) languages depends largely on the development of environments that facilitate the specification and integration of constraints in the sema...
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The development of more powerful Concurrent constraint logic programming (CCLP) languages depends largely on the development of environments that facilitate the specification and integration of constraints in the semantics of a logic program and automatically extract the inherent parallelism of logicprogramming. This paper presents a novel method for automating the parallel AND/OR execution of CCLP applications. This method consists of two stages. The first stage translates a logic program into an equivalent Attribute Grammar providing a common language in which the specifications of constraints and the semantics of a logic program can be expressed. The second stage evaluates this Attribute Grammar using MPAGE, a Multipass Parallel Attribute Grammar Evaluation algorithm. Support for the processing of constraints in the logic program is provided with the creation of a dependency graph between the variables of a logic rule during the first stage. Using this dependency graph MPAGE delays, if necessary, the evaluation of variables in a constraint until they become bound at some later point in processing. As a result our method supports rule representations in CLP languages with no restrictions on the ordering of subgoals. Furthermore, during execution MPAGE allows single rules in a CLP program to deal with multiple assignments of bindings, thus generating a minimal number of processes. Finally, this method is independent from the underlying hardware and its memory organization, therefore it can be implemented on both shared and distributed memory systems.
A commodity auction market provides a trading intermediary whose role is to find optimal trade matching between buyers and sellers that satisfies their trading constraints. Some commodity auction markets utilize forms...
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A commodity auction market provides a trading intermediary whose role is to find optimal trade matching between buyers and sellers that satisfies their trading constraints. Some commodity auction markets utilize forms of electronic trading intermediary systems in order to improve the efficiency and effectiveness of trading of huge volumes of transactions during short periods of time. Previous research works on electronic trading intermediary systems focus on the maximization of the trade volume obtained by satisfying mainly price and quantity constraints. The principal restriction of these approaches is that the heterogeneity of the commodity is ignored or at least not significantly considered. The objective of the study in this paper is to propose a computable mechanism of trading intermediaries for commodity auction markets, supporting not only ordinary trading constraints of prices and quantities but also other qualitative and quantitative constraints on the commodity properties and trading conditions.
This paper presents the design and implementation of a distributed advisory system which helps different human experts in the management and control of traffic within railway stations and along railway branches. Our a...
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This paper presents the design and implementation of a distributed advisory system which helps different human experts in the management and control of traffic within railway stations and along railway branches. Our approach allows the management of a whole railway line in a modular, expandable and scalable way. The scheduling of trains along a railway line is performed by several modules each one controlling a certain number of resources. These modules solve the scheduling of trains by interacting and communicating with each other. Each module has to deal with temporal constraints, priority between trains and constraints due to the structure of the station and railway branches. Our approach is based on the constraint logic programming (CLP) paradigm for solving the constraints involved in the problem. Therefore, this paper shows the versatility and adequacy of the CLP approach for the problems of this type. (C) 1997 Elsevier Science Ltd.
Vehicle-fleet scheduling is one of the most commonly occurring problems of transport management. In this paper a new approach facing the problem is introduced. It draws upon the combination of the advantages of Constr...
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Vehicle-fleet scheduling is one of the most commonly occurring problems of transport management. In this paper a new approach facing the problem is introduced. It draws upon the combination of the advantages of constraint logic programming (CLP) with the benefits of local search in order to obtain satisfactory results with respect to execution time. CLP is used for generating an initial feasible solution and then for checking every intermediate solution obtained from local search so that it is in accordance with the constraints of the problem. Local search is implemented for the minimisation of the cost of the initial solution. Several local search methods were tested on various cases of the problem and the results obtained are discussed and compared with respect to the cost of the solution and the execution time. (C) 1997 Elsevier Science B.V.
For many real-life problems naturally modelled as constraints systems, we have to manage dynamically systems of constraints. So, a model based on the formalism of finite constraint Satisfaction Problems (CSPs) (Montan...
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For many real-life problems naturally modelled as constraints systems, we have to manage dynamically systems of constraints. So, a model based on the formalism of finite constraint Satisfaction Problems (CSPs) (Montanari, 1974) has been proposed with Dynamic CSPs (DCSPs) to handle this kind of problem (Dechter and Dechter, 1988;Janssen et al., 1990). Some classical techniques defined in the field of CSPs are usable in DCSPs, but the management of dynamicity induces new problems such as management of over-constrained systems and consistency maintenance. At present, constraintprogramming tools generally do not offer a framework for integrating dynamic constraints. The purpose of this paper is to introduce an efficient way to solve DCSPs based on a logical approach. We use and extend Ordered Binary Decision Diagrams (OBDDs) (Bryant, 1986) and propose a particular coding for dynamicity. We show that our approach allows to solve some major questions in the field of DCSPs. (C) 1997 Elsevier Science B.V.
In this paper we discuss the integration of logic, modeling, and programming in order to solve problems in operations research, artificial intelligence, and decision support programming in general. Our goals are to in...
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In this paper we discuss the integration of logic, modeling, and programming in order to solve problems in operations research, artificial intelligence, and decision support programming in general. Our goals are to integrate modeling into the larger programming scheme of things and, conversely, to inject programming into modeling. To accomplish these ends, we use the language 2LP, which is based on ideas from constraint logic programming. This leads to a technologically open way to handle problems, one which supports flexible treatment of goal programming, hybrid MIP/local search algorithms, libraries for distributed processing, disjunctive programming, etc. An additional advantage of the programming language approach is that problem solving and model management can be abetted by software engineering techniques. In this paper, by means of variations on a single example, we will illustrate how the logical connectives and linear constraints interact in the solution of a linear program, a goal program, a disjunctive program, a branch and bound search, a randomized shuffle algorithm, and a parallel solution to a model with stochastic data.
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