Modelling Web Navigation by Statechart(4)

UML,OOP,面向对象

Figure5.ParameterizedOR

Eventscanaffectstatesglobally.Thisglobaleffectofalloccurredeventisdescribedasbroadcastingofeventstoallpartsofthesystem.Allactivities/eventsareconsideredinstant(zerotime),sosynchronizationcanbesupportedbythetriggeringofsomelimitingeventsonallconcurrentpar-titions.

WewillalsousethesuggestedparameterizedORexten-siontostatechart[3]forsituationswherelargequantityofsimilarstatesareencountered(Figure5).Eventewillhap-penwithaparameterparam.InB,paramwillbeevaluatedandthesystemwilltransittotheappropriatestate,outofthegroupofstatesstateparam,basedonthisevaluation.Thereareproblemsofundeterminedstatewhenevents/activityarede nedaszerotime,asdescribedin[3,5,8].Wewilltakethemicro-stepapproach[8]tosolvedthisproblem.

3WebNavigationAnalysis

3.1WebPage

Awebpageisde nedasthesequenceofHTMLrepliedbythewebservertoaclientmakingarequestofaURLthroughHTTP.Othernavigationrelatedmaterialsinthewebpage,suchasscriptsandclientsideprograms,arecon-sideredcomponentsofthewebpage.Non-navigationre-latedmaterials,suchasgraphicsoraudioclipscontainedinthewebpage,arenotconsideredinthisanalysis.

AstaticwebpageisawebpagethatretainsthesameHTMLforalltheclientrequestsofthesameURL.Itmustalsocontainnoreactiveorexecutablecomponents.Adynamicwebpageisde nedasawebpagethatre-turnsdifferentHTMLforclientrequestsofthesameURL(serversidedynamics),orcontainsreactiveorexecutablecomponents(clientsidedynamics).

3.2Hyperlink

NavigationintheWWWisdonebyactivatinghyper-links.Hyperlinksaredirectionallinksbetweenasourceandatargetwebpage,whichcanbethesamepage,solinkingtodifferentsectionsofthesamewebpageispossible.Whenahyperlinkisactivated,thecurrentwebpageinviewwillbereplacedbythetargetwebpage.Ahyperlinkcanbeinformoftextstrings,graphicsorvideo,activatedexplicitlybytheusers,usingamouseclickforexample.Hyperlinkscanalsobeincludedinclientsideprograms/scripts,tobeinvokedautomaticallybythebrowseronsomeprede nedevents.Examplesoftheseeventsincludestimeout,mousemove-mentsandwindowfocus.Asinhypertext,thesequenceofhyperlinkactivation,nomatterbymouseclickorotherevents,isthenavigationpath.

3.3Webbrowsereffects

Inadditiontothenavigationprovidedbyhyperlinks,webbrowserscanprovideadditionalnavigationfunctionsthatisoutofcontrolofthewebpages,suchasscrolling,back,forwardbuttonsandahistorylist.Wedonotintendtodis-cussionthisformofnavigationhere,sowebnavigationbywebbrowserfunctionsareoutofscopeforthispaper.

3.4Intra-pageNavigation

Thisformofwebnavigationinvolvesonlyonewebpage.Inawebpage,hyperlinkscanbede ercanalsoscrolltodifferentsectionsofthepageifthepageisdisplayedinascrollbarenabledframeorwindowtoobtainthesamere-sult.

3.5Inter-pageNavigation

Thismostcommonformofwebnavigationisbyactivat-ingahyperlinkonasourcewebpage,tojumptoatargetwebpagewhichthehyperlinklinksto.

3.6Frame-basedNavigation

Framesinsideabrowserwindowmakesconcurrentviewingofwebpagespossible(Figure6).Abrowserwin-dowcanbedividedintoframes,eachcontainingasepa-ratewebpageforviewing.Thecontainedwebpagescanbeanotherwebpagecontainingframes.Navigationwithinaframecanhappenindependently.Navigationoutofaframedwebpagecanalsobedonebyactivatingahyper-linkthatspeci esthetargetistoreplacethewholeframedpage.Allframesinawindowarecreatedanddestroyed