Unconstrained Constraint Programming

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1、Volume8(4)1995,pp.329{354UnconstrainedConstraintProgrammingJ.E.A.vanHintumCWI,DepartmentofInteractiveSystemsP.O.Box94079,1090GBAmsterdam,theNetherlandse-mail:hansh@cwi.nlTheexpressivepowerandusabilityofaconstraintsystemdependsontwothings;thedegreeinwhichtheconstraintsystemissuitedforthee

2、nvironmentitisusedinandtheeasewithwhichaprogrammermayadaptthebehaviorofthecon-straintsystemtohisownneeds.ThisarticlewillshowthattheMadeconstraintsystemisverywellsuitedfortheenvironmentitisdesignedfor(multimediaappli-cations)andthattheprogrammerisabletoadaptthebehavioroftheconstraintsyste

3、monallitsthreeimportanttasks:triggering,propagationandsatisfaction.Acentralroleinthisarticleisplayedbytheconstraintnetworkasthisisalsothecentralpartoftheconstraintsystem.Themoreaprogrammerisabletotunetheactionperformedbytheconstraintsystemontheconstraintnetwork,themoreexpressiveconstrain

4、tscanbedenedbythatsameprogrammer.1.IntroductionThispaperdiscussestheconstraintsystemdevelopedfortheMadeprogram-mingenvironment.Constraintscanbeofgreatpracticaluseinmultimediaapplications,butonlyiftheyaredesignedcorrectlyforuseinthemultime-diaarea.Then,amultimediaconstraintsystemmaysigni

5、cantlyreducetheamountofworkneededtoconstructamultimediaapplication;constraintshavetobedeclaredanddenedonceandaremaintainedautomaticallyineverysit-uationandatalltimes.Thisimprovesreadabilityandmaintenanceoftheapplication.Madeisadedicatedobjectoriented,multimediaprogramming++++environmen

6、tusingtheprogramminglanguagemC(basedontheCpro-gramminglanguage)whichprovidestheprogrammerwithtoolsandutilitiestowritemultimediaapplicationseasily.ForadetaileddescriptionofMadethereaderisreferredto[1,2,13,16].TheobjectiveoftheMadeconstraintsystemistoprovideconstraintswhichdonotrequireanya

7、daptationstotheobjectswhicharetobeconstrained.This329means,thatwheneveraprogrammerwantstoconstrainanumberofobjects,thespecicationoftheseobjectsremainsuntouched.Theprogrammeronlyhastodenethenewconstraintobjectsandactivatetheconstraintsystem.Thiscanberealizedbydelegation,