Enforcing local consistencies in cost function networks is performed by applying so-called Equiva... more Enforcing local consistencies in cost function networks is performed by applying so-called Equivalent Preserving Transformations (EPTs) to the cost functions. As EPTs transform the cost functions, they may break the property that was making local consistency enforcement tractable on a global cost function. A global cost function is called tractable projection-safe when applying an EPT to it is tractable and does not break the tractability property. In this paper 1 , we prove that depending on the size r of the smallest scopes used for performing EPTs, the tractability of global cost functions can be preserved (r = 0) or destroyed (r > 1). When r = 1, the answer is indefinite. We show that on a large family of cost functions, EPTs can be computed via dynamic programming-based algorithms, leading to tractable projection-safety. We also show that when a global cost function can be decomposed into a Berge acyclic network of bounded arity cost functions, soft local consistencies such as soft Directed or Virtual Arc Consistency can directly emulate dynamic programming. These different approaches to decomposable cost functions are then embedded in a solver for extensive experiments that confirm the feasibility and efficiency of our proposal.
This paper describes our experience with a simple modeling and programming approach for increasin... more This paper describes our experience with a simple modeling and programming approach for increasing the amount of constraint propagation in the constraint solving process. The idea, although similar to redundant constraints, is based on the concept of redundant modeling. We introduce the notions of CSP model and model redundancy, and show how mutually redundant models can be combined and connected using channeling constraints. The combined model contains the mutually redundant models as sub-models.
Constraint satisfaction is one of the major areas in AI that has important real-life applications... more Constraint satisfaction is one of the major areas in AI that has important real-life applications. Lee et al. propose E-GENET, a stochastic solver for general constraint solving based on iterative repair. Performance figures show that E-GENET compares favorably against tree-search based solvers in many hard problems. On the other hand, global constraints have been shown to be very effective in modeling complicated CSP's. They have also improved substantially the efficiency of tree-search based solvers in solving real-life problems.
The paper describes a simple modeling and programming approach for speeding up constraint propaga... more The paper describes a simple modeling and programming approach for speeding up constraint propagation. The idea, although similar to redundant constraints, is based on the concept of redundant modeling. We define CSP model and model redundancy formally, and show how mutually redundant models can be combined and connected using channeling constraints. The combined model contains the original but redundant models as sub-models.
Abstract Based on the notions of viewpoints, models, and channeling constraints, the paper introd... more Abstract Based on the notions of viewpoints, models, and channeling constraints, the paper introduces model induction, a systematic transformation of constraints in an existing model to constraints in another viewpoint. Meant to be a general CSP model operator, model induction is useful in generating redundant models, which can be further induced or combined with the original model or other mutually redundant models.
The task at hand is to tackle Constraint Satisfaction Problems (CSPs) defined in the sense of Mac... more The task at hand is to tackle Constraint Satisfaction Problems (CSPs) defined in the sense of Mackworth [4]. This paper aims to take a first step towards a CSP-based module systems for constraint programming languages and modeling tools. The call for such a system is two-fold. First, most existing constraint programming languages have some sort of module systems, but these systems are designed for the underlying languages.
An analytical study of puzzle selection strategies for the esp game
Abstract" Human computation" represents a new paradigm of applications that take advantage of peo... more Abstract" Human computation" represents a new paradigm of applications that take advantage of people's desire to be entertained and produce useful metadata as a by-product. By creating games with a purpose, human computation has shown promise in solving a variety of problems that computer computation cannot currently resolve completely.
Abstract: VISOLE (Virtual Interactive Student-Oriented Learning Environment) is a learning style ... more Abstract: VISOLE (Virtual Interactive Student-Oriented Learning Environment) is a learning style that uses a virtual game environment to facilitate learning. The web-based game environment is a simulation of the real world where students participate as “citizens” and take part in shaping the development of the virtual world.
Abstract: In this paper, we report the design and implementation of a constraint-based interactiv... more Abstract: In this paper, we report the design and implementation of a constraint-based interactive train rescheduling tool, a project in collaboration with the International Institute for Software Technology, United Nations University (UNU/IIST), Macau. We formulate train rescheduling as constraint satisfaction and describe a constraint propagation approach for tackling the problem. Algorithms for timetable verification and train rescheduling are designed under a coherent framework.
Abstract The paper describes the design and implementation of a constraint-based nurse rostering ... more Abstract The paper describes the design and implementation of a constraint-based nurse rostering system using a redundant modeling approach. Nurse rostering is defined as the process of generating timetables for specifying the work shifts of nurses over a given period of time. This process is difficult because the human roster planner has to ensure that every rostering decision made complies with a mixture of hard hospital rules and soft nurse preference rules.
The paper introduces value precedence on integer and set sequences. A useful application of the n... more The paper introduces value precedence on integer and set sequences. A useful application of the notion is in breaking symmetries of indistinguishable values, an important class of symmetries in practice. Although value precedence can be expressed straightforwardly using if-then constraints in existing constraint programming systems, the resulting formulation is inefficient both in terms of size and runtime.
A common type of symmetry is when both variables and values partition into interchangeable sets. ... more A common type of symmetry is when both variables and values partition into interchangeable sets. Polynomial methods have been introduced to eliminate all symmetric solutions introduced by such interchangeability. Unfortunately, whilst eliminating all symmetric solutions is tractable in this case, pruning all symmetric values is NP-hard. We introduce a new global constraint called SigLex and its GAC propagator for pruning some (but not necessarily all) symmetric values.
Abstract Heuristic repair algorithms, a class of local search methods, demonstrate impressive eff... more Abstract Heuristic repair algorithms, a class of local search methods, demonstrate impressive efficiency in solving some large-scale and hard instances of constraint satisfaction problems (CSPs). We draw a surprising connection between heuristic repair techniques and the discrete Lagrange multiplier methods by transforming CSPs into zero-one constrained optimization problems. A Lagrangian-based search scheme LSDL is proposed.
Recently Lee, Stuckey and Tam have shown the advantages of incorporating stochastic solvers into ... more Recently Lee, Stuckey and Tam have shown the advantages of incorporating stochastic solvers into constraint logic programming (CLP) systems. Their approaches, while efficient, both suffer from some form of incompleteness and complication in semantics. This paper proposes a generalization of these previous efforts by using stochastic methods to guide and speed up the search of derivation trees for successful branches.
Abstract Typically local search methods for solving constraint satisfaction problems such as GSAT... more Abstract Typically local search methods for solving constraint satisfaction problems such as GSAT, WalkSAT, DLM, and ESG treat the problem as an optimisation problem. Each constraint contributes part of a penalty function in assessing trial valuations. Local search examines the neighbours of the current valuation, using the penalty function to determine a “better” neighbour valuation to move to, until finally a solution which satisfies all the constraints is found.
Abstract Van Emden's incremental queries addresses the inadequacy of current Prolog-~ yle queryin... more Abstract Van Emden's incremental queries addresses the inadequacy of current Prolog-~ yle querying mechanism for interactive problem-solving. In the context of constraint logic programming, incremental queries involves adding or deleting constraints. This paper presents an implementation scheme IQ of incremental queries in Constraint Pandora. We use Van Hentenryck and Le Provost's scheme (VHLP-scheme hereafter) as a starting point.
Abstract As a logic programming language, Prolog has shortcomings. One of the most serious of the... more Abstract As a logic programming language, Prolog has shortcomings. One of the most serious of these is in arithmetic. CLP (R), though a vast improvement, assumes perfect arithmetic on reals, an unrealistic requirement for computers, where there is strong pressure to use oatingpoint arithmetic. We present an adaptation of CLP (R) where the errors due to oating-point computation are absorbed by the use of intervals in such a way that the logical status of answers is not jeopardized.
Abstract Existing interval constraint logic programming languages, such as BNR Prolog, work under... more Abstract Existing interval constraint logic programming languages, such as BNR Prolog, work under the framework of interval narrowing and are deficient in solving linear systems, which constitute an important class of problems in engineering and other applications. In this paper, an interval linear equality solver, which is based on generalized interval arithmetic and Gaussian elimination, is proposed.
Abstract In the past decade, there has been much research e ort dedicated to combine the object-o... more Abstract In the past decade, there has been much research e ort dedicated to combine the object-oriented programming paradigm and the logic programming paradigm. Most of this e ort sheds light upon the philosophy of multiparadigm programming as a near ideal mental model for a wide class of problem domains. In this paper we propose a scheme for object and logic integration| the OLI scheme.
The Effectiveness of Teachers’ Facilitation in Using Game Elements to Motivate Students’ Participation in CSCL discussion
Abstract: This study investigates whether teachers' facilitation was conducive to the effective u... more Abstract: This study investigates whether teachers' facilitation was conducive to the effective use of game elements on a CSCL platform in motivating students' participation in CSCL discussion. The learning process of 1,112 Grade Five students in 13 Hong Kong and seven Taipei elementary schools was studied. Divided into groups, each of which composed of six to eight students of two places, the students were engaged in project learning for four months.
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Papers by Jimmy Lee