Abstract
The presentation of constraints in a usable form is an essential aspect of Constraint Logic Programming (CLP) systems. It is needed both in the output of constraints, as well as in the production of an internal representation of constraints for meta-level manipulation. Typically, only a small subset\(\tilde x\) of the variables in constraints is of interest, and so an informal statement of the problem at hand is: given a conjunction\(c(\tilde x,\tilde y)\) of constraints, express the projection\(\exists \tilde y c(\tilde x,\tilde y)\) ofc onto\(\tilde x\) in the simplest form.
In this paper, we consider the constraints of the CLP(R) system and describe the essential features of its projection module. One main part focuses on the well-known problem of projection inlinear arithmetic constraints. We start with a classical algorithm and augment it with a procedure for eliminating redundant constraints generated by the algorithm. A second part discusses projection of the other object-level constraints: equations over trees and nonlinear equations. The final part deals with producing a manipulable form of the constraints, which complicates the projection problem.
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Joxan Jaffar, Ph. D.: He received his Ph. D. from Monash University, was a lecturer there from 1982 to 1986, and since 1986 has been with the IBM T. J. Watson Research Center. He is currently a project leader at IBM, and the Area Editor for Theory, Journal of Logic Programming.
Michael Maher, Ph. D.: He received his Ph. D. in computer science from the University of Melbourne. He is currently a research staff member of the IBM T. J. Watson Research Center. His research interests involve constraint systems, logic programming and databases.
Peter J. Stuckey, Ph. D.: He has been a lecturer in Computer Science at the University of Melbourne since 1990. His research interests include logic programming, deductive databases and constraint programming. He is one of the authors of the constraint logic programming languages CLP(R). Peter holds a B. Sc(Hons) and Ph. D. in computer science from Monash University. He is a member of the Association of Logic Programming.
Roland H. C. Yap, Ph. D.: He is a researcher at the University of Melbourne. He is currently finishing a Ph. D. at Monash University. His research interests include constraints, logic programming, programming languages, compilers and computational molecular biology.
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Jaffar, J., Maher, M.J., Stuckey, P.J. et al. Projecting CLPR constraints. New Gener Comput 11, 449–469 (1993). https://doi.org/10.1007/BF03037187
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DOI: https://doi.org/10.1007/BF03037187