Modelling Web Navigation by Statechart(2)

UML,OOP,面向对象

VBScript,JAVAandActiveX,provideotherwaystocon-troltravelingbetweendifferentwebpageswithoutclick-ingalink.DynamicHTML,ActiveXcomponentsarealsowidelyemployedtochangethecontentandhyperlinksofthecurrentlydisplayingwebpage.

Concurrentdisplayofwebpagesispossiblebytheuseofframesandwindows.Synchronizationbetweentheconcur-rentlydisplayedwebpagescanbeachievedwithfunctionsoftheclientsidescriptsandcontrolprograms.Detaileddis-cussiononnavigationofwebpagesisinSection3.

2.2WebModeling

Itisnothardtorealizethatthecomplicationsaddedbytheabovediscussedwebfeaturesmakesthewebpageandlinksnotnecessarilyadirectmappingfromtheinformationfragmentsandrelationshipsinhypertext.Somodelingtech-niquesusedinhypertext[13,16]maynotbedirectlyappli-cable.Theresearchesonwebmodelingarecomparativelyfewtothehypertextmodelresearches.

Conallen[2]discussedusingthecommonbehaviorpackageinUni edModelingLanguage(UML)[10]tomodelthebusinesslogicinwebapplications.Clientpages,Serverpages,FormsandFramesarede nedasclassesinUML,withtheircontentsmodeledasstereotypedattributesoftheclass.Linksbetweenwebpagesaremodeledasasso-ciationsbetweenthelinkedclasses.Themodelingisviewedfromtheperspectiveofbusinesslogicinstructureandfunc-tionalview,sosomeuserinterfaceattributesaffectingpre-sentationandbrowsingsemanticsareintentionallyleftoutfromthismodel.Thesuggestedmodelingmethodcanbeusedasacomplimenttoourmodeltosupplyinformationaboutbusinesslogic.

Onthesametrackwithus,HMBS[15](HypertextModelBasedonStatecharts)usesstatechart(seesec-tion2.3)asamodelingtool.HMBSaimstosupportbe-havioralmodelinginthedesignofhypermediabythesug-gestedmodel.Anhypermediaauthoringtoolisalsodevel-opedtoachievethisgoal.Inthemodel,hypermediapagesaremappedtostatesinstatechartbyamappingfunction,whichcanbealteredfordifferentstatechartstomakeabstractionofphysicalpagespossible.isheldstaticforaparticularstatechart,andcannotbechangedduringnav-igation.Thisfreedominde nitionof

maybefeasibleinhypermediaauthoringasthedesignercande nearbi-trarily,andthenalldevelopmentthereafterwilladheretoit.Problemarisesifmultiplepartieswishtomodelanexistingsetofhypermediapages,asitisnotclearthathowcanbede nedinaconsistentwaybydifferentmodelers,theremaybevastdifferencebetweenresultantmodelsofthesamesetofwebpages.Wewillsolvethisproblembyprovidingaconsistentwaytomapwebpagesinournavigationmodel.HMBSismoreconcernedwiththehierarchicalstruc-turingofhypermediapagesthanothernavigationmethodsbetweenpages.VisibilitylevelLisde nedtomanagethevisibility(state)ofhierarchicalpagesduringhierarchicalnavigation.Allothernavigationmethodsaregenerallyde-scribedaseventsrepresentingtransitionofstates,withnodetailsondifferentkindsofeventsgiven.Treatingallkindsofeventsequallywillintroducedif cultiesinmodelingdif-ferentkindsofhyperlinksintheweb,suchasbetweenanordinaryhyperlinkandaserversidescriptwhichactsonparameterssentalongwiththehyperlinktransition.Wean-alyzeandidentifydifferentwaystomodeldifferentkindsofhyperlinkinSection3and4.

ItisalsonotclearthathowcantheHMBSmodelsupportmodelingofdynamichypermediapages,whichareusedex-tensivelyincontemporarywebdevelopment.Evenwiththechangeablemappingfunction,itisimpossibletomodelphysicalhypermediapagesthatchangestheircontentdur-ingnavigation,orcontainsdifferentcontentwhendifferentlinksareused(events)toenterthepage.Thisisbecausemustbeheldstaticinanavigationsession.Thisises-peciallytrueforthosepagesthatchangestheirlinks(tran-sitions)tootherpages(states)duringnavigation,llowupworksofHMBS,themodelingfocushadshiftedtotimingandsynchronizationofmultimediacontentinhyperdocuments[11,12],andthedevelopmentofhyperdocumentauthoringsoftware[14],sotheaboveproblemsstillsremainunresolved.InSection4,wewilldiscussedhowtoovercomeallthesedif cultiesbyournavigationmodel.

Therearealsosomeresearchesonhypermediamodel-ing,whichisthemodelingofmultimediahyperlinkedcon-tents.HMData[6]isanobjectorientedmodelingmethodforstorageandretrievalofhypermedia.Thismodularap-proachdiscourageslinkagesbetweenindividualelementsofdifferentmodules,andmaynotbesuitableforthewebwhereextensive,spaghettilinkagesbetweenwebpagesofdifferentsitesisthenorm.EFSM[7]isanextended nitestatemachinetomodeltemporalsynchronizationoftem-poralinteractivewebcontent.Theanalysisismainlyfo-cusedinsynchronization,andthemodelmaybeblownuptounmanageablesizeifthequantityofmediaislargeandlinkagebetweenmediaextensive,duetothenatureof nitestatemachine.

Anotherapproachingtomodelthenavigationofthewebisbyusingwebpagecontentinadditiontotheirintra-linkages[1,9].Thegeneralideaistousethecontentsim-ilaritybetweenpagestostructurethem,providingabetterunderstandingandsenseoforientationfortheuserofthein-formationspace.Thesemodelsgivegeneralshapeofthein-formationspace,browsingthewebpagesinan“overview”mode,andisnotsuitableforanalysisonbrowsingseman-ticsbetweenindividualpages.