Treść książki
Przejdź do opcji czytnikaPrzejdź do nawigacjiPrzejdź do informacjiPrzejdź do stopki
1.2Newformsofparticipation—pushorpull?
21
1.2
Newformsofparticipation—pushorpull?
OnenotablechangeintroducedbyWeb2.0patternsinsoftwaredevelopment
istheswitchfromthepullarchitecturetothepusharchitecture.Generally,
itisnotanimprovement,butmerelyaphilosophicalchange.Formany
yearsproponentsofbotharchitectureshavebeenwagingareligiouswar
overmeritsofbothapproaches.Brieflyspeaking,thepullarchitecturerefers
toasituationwhereinformationisactivelysearchedandretrieved(pulled)
fromthenetwork.AclassicalexampleofthepullarchitectureistheWorld
WideWeb,whereuserssendHTTPrequeststoserversinordertoobtain
documents.Incontrast,inthepusharchitecturearecipientofinformation
waitspassivelyandinformationisbeingautomaticallydelivered(pushed)by
anunderlyingframework.Anexampleofthepusharchitectureiselectronic
mail,wheredesiredinformationispushedintorecipient?smailboxbyan
underlyingmailtransferprotocol.Theparticularchoiceofonearchitecture
overanotherhasmanyimportantconsequencesoutlinedbelow.
•openness:pullispubliclyavailableandcanbeperformedbyanyone,
pushrequirespriorregistration,subscription,oranyothertypeof
relationship,
•demandanticipation:pullisunpredictableanddifficulttoforecast,
pushislimitedtoaknownnumberofsubscribes,
•deliverability:pullisusuallybasedonrequest-responsesemanticsand
canbearmoredwithdeliveryguarantees,pushmustusesomekindof
acknowledgmentprotocoltoguaranteedelivery,
•updates:pullislessscalablew.r.t.updatesduetoconstantpolling
forupdates,pushismorescalableasupdatescanbemanagedby
notifications,
•networkbandwidth:pullissuitedforfrequentpollingbecauseresponse
isdeliveredforeveryrequest,pushissuitedforinfrequentupdates
becausenotificationsaresentonlywhennecessary.
InWeb2.0environmentthepusharchitectureisstronglypreferredover
thepullapproach.Pushingdatatousersistheleadingcharacteristicoftech-
nologiessuchasblogs,podcasts,instantmessaging,mashups,andpipes.The
departurefromthemodelinwhichauserisactivelysearchingforinforma-
tioninfavorofinformationactivelysearchingforauserresultsinadrastic
improvementofqualityandreliabilityofinformationobtainedbyauser.
Thisphenomenoncanbeexplainedasfollows.Aswehavenoticedearlier,
thepushapproachisbasedonasubscription(orasimilarrelationship)
toadatasource.Subscriptionsmaybemanagedindividuallyforeachser-
vice(apodcastorablog),butmostusersrelyoncentralizedsubscription
