a method for the construction of robust class hierarchiesnew

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1、AMethodfortheConstructionofRobustClassHierarchiesArneFrickRainerNeumannWolfZimmermann18thJune1996AbstractWeintroduceamethodfortheconstructionofrobustclasshierarchies.Thebaseofthisconstructionisarigorousdenitionofinheritance.Therearefourpossibleinheri

2、tancerelationships.Atleasttwoofthemturnedouttobeimportantinpractice.Accordingtothisforthersttime,conditionsforthecorrectuseofpolymorphismaregiven.Weshowhowinheritancehierarchiescanbeconstructedinasystematicandrigorousway.1IntroductionTheparadigmofobject

3、-orientedprogramminghasprovidedalargenumberofmethodsforthedesignandtheimplementationofapplications,mostofwhichdonotprovideasolidandformalbasisforcorrectnessproofs.Thoughthemethods[1,5]helptodevelopasystem,thereisnosupporttoassertorprovecertainproperties.

4、Onereasonforthisis,thatbasicconceptslikeinheritance,polymorphismandgenericityarenotdeterminedinaformalmanner.Thismakessense,ifoneissalingdesigntools,becausethiswaysomekindoflanguageindependenceiseasiertoreach.ButevenformalmethodslikeObject-Zalsofailbecau

5、seofthislackofformaldenitions.Wethereforehavetorecognize,thataftermorethanonedecadeofobject-orientedmodelingbasicconceptsarenotreallyunderstoodordescribedinamathematicalway.Whatismissing,isamethodforthecorrectdevelopmentofobject-orientedsystems.Although

6、therequirementsneededtoprovidecorrectsystemsorclasslibrarieswereshownin[2],thereisstillneedforamethodforthesystematicconstructionofsuchsystems.Thetasknowistoconstructamethodwhereacorrectdevelopmentprocessleadstoacorrectsystem.MeyersDesignbyContract[4]iso

7、nesteptowardsthisgoal.Linkagebetweenobjectsisdescribedbypre{/postconditionsandinvariants.Butstilltheuseofinheritance,polymorphismorgenericitymayleadtoincorrectsystems{theglobalsystemcorrectnessmaybedestroyedbylocallycorrectclasses.Thispapernowdescribes,h

8、owobject-orientedsystemsmaybedesignedsothatviolationsoftheglobalsystemcorrectnesswillbedetectedatcompilationtime.Thismethodismentionednottoreplacebuttosupportexistingmethodsbygivenformaldescriptionsofbasicconcepts.Theremai