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Date: Tue, 10 Dec 1996 03:25:24 GMTServer: NCSA/1.4.2Content-type: text/html<html><head><TITLE>Constraint Hierarchies</title></head><body><H2>Constraint Hierarchies</H2><p>Authors: Alan Borning, Bjorn Freeman-Benson, and Molly Wilson<p><em>Lisp and Symbolic Computation</em>, Vol. 5 No. 3, (September 1992),pages 223-270.<P>Reprinted in <em>Constraint Programming</em>, B. Mayoh, E. Tougu, J.Penjam (Eds.), NATO Advanced Science Institute Series, Series F: Computerand System Sciences, Vol 131, Springer-Verlag, 1994, pages 75-115.<P><hr><H3>Abstract</H3>Constraints allow programmers and users to state declaratively a relationthat should be maintained, rather than requiring them to write proceduresto maintain the relation themselves. They are thus useful in suchapplications as programming languages, user interface toolkits, andsimulation packages. In many situations, it is desirable to be able tostate both <em>required</em> and <em>preferential</em> constraints. Therequired constraints must hold. Since the other constraints are merelypreferences, the system should try to satisfy them if possible, but noerror condition arises if it cannot. A <em>constraint hierarchy</em>consists of a set of constraints, each labeled as either required orpreferred at some strength. An arbitrary number of different strengths isallowed. In the discussion of a theory of constraint hierarchies, wepresent alternate ways of selecting among competing possible solutions, andprove a number of propositions about the relations among thesealternatives. We then outline algorithms for satisfying constrainthierarchies, and ways in which we have used constraint hierarchies in anumber of programming languages and systems.<P><HR><P>Click <!WA0><a href="ftp://cs.washington.edu/pub/constraints/papers/constraint-hierarchies-lisp-symb-comp.ps.Z">here</a> to get the postscript file.<P>Return to <!WA1><a href="http://www.cs.washington.edu/research/projects/weird/www/index.html">Constraints home page</a>⌨️ 快捷键说明
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