NewprogramminglanguageautomaticallycoordinatesinteractionsbetweenWebponents 23December2014,byLarryHardesty InadditiontomakingWebapplicationseasiertowrite,Ur/Webalsomakesthemmoresecure."Let'ssayyouwanttohaveacalendarwidgetonyourWebpage,andyou'regoingtousealibrarythatprovidesthecalendarwidget,andonthesamepagethere'salsoanadvertisementboxthat'sbasedoncodethat'sprovidedbythework,"Chlipalasays."Whatyoudon'twantisfortheworktobeabletochangehowthecalendarworksortheauthorofthecalendarcodetobeabletointerferewithdeliveringtheads."Ur/Webautomaticallyprohibitsthatkindofunauthorizedessbetweenpageelements. Credit:iStock/MIT AWebpagetodayistheresultofanumberofponents—likecascadingstylesheets,XMLcode,adhocdatabasequeries,andJavaScriptfunctions.Forallbutthemostrudimentarysites,keepingtrackofhowthesedifferentelementsinteract,refertoeachother,andpassdatabackandforthcanbeatime-consumingchore. InapaperbeingpresentedattheAssociationforComputingMachinery'sSymposiumonPrinciplesofProgrammingLanguages,AdamChlipala,theDouglasRossCareerDevelopmentProfessorofSoftwareTechnology,describesanewprogramminglanguage,calledUr/Web,thatletsdeveloperswriteWebapplicationsasselfcontainedprograms.Thelanguage'piler—theprogramthatturnshigh-levelinstructionsintomachine-executablecode—thenautomaticallygeneratesthecorrespondingXMLcodeandstylesheetspecificationsandembedstheJavaScriptanddatabasecodeintherightplaces. Typing,scoping Ur/Web'sabilitytobothprovidesecurityprotectionandcoordinatedisparateWebtechnologiesstemsfromtwopropertiesitshareswithmostfull-blownprogramminglanguages,likeC++orJava.Oneisthatitis"stronglytyped."ThatmeansthatanynewvariablethataprogrammerdefinesinUr/Webisconstrainedtoaparticulardatatype.Similarly,anyspecificationofanewfunctionhastoincludethetypeofdatathefunctionactsonandthetypeofdataitreturns. putingthevaluetoreturn,thefunctionmayneedtocreatenewvariables.(Afunctionthatreturnedanaverageofvaluesinadatabase,forinstance,wouldfirstneedtocalculatetheirsum.)Butthosevariablesareessibletotherestoftheprogram.Thisisthesecondproperty,knownas"variablescoping,"becauseitlimitsthescope—thebreadthofessibility—ofvariablesdefinedwithinfunctions. "Youmightwanttowritealibrarythathasinsideofitasprivatestatethedatabasetablethatrecordsusernamesandpasswords,"Chlipalasays."Youdon'twantanyotherpartofyourapplicationtobe 1/3 abletojustreadandoverwritepasswords.MostWebframeworksdon'tsupportthatstyle.Theyassumethateverypartofyourprogrampleteesstothedatabase." Typinghelpswithsecurity,too.ManyWebdevelopmentframeworksgeneratedatabasequeriesinsuchawaythatsomeoneostensiblyloggingintoawebsitecantypecodeintotheusernamefieldthatinfactoverwritesdatainthedatabase.WithUr/Web,usernameswouldconstitutetheirowndatatype,whichwouldbehandledmuchdifferentlythandatabasequeries. usedinapositionwheretablepropertieswouldhaveanymeaning,soyoudon'thavetobothersettingthose." Moreinformation:Paper:"Ur/Web:AsimplemodelforprogrammingtheWeb" ProvidedbyMassachusettsInstituteofTechnology Meetingexpectations TypingisalsowhatenablescoordinationacrossWebtechnologies.SupposethatabitofJavaScriptcodeissupposedtoactondatafetchedfromadatabaseandthattheresultissupposedtobedisplayedonaWebpageatalocationdeterminedbysomeXMLcode.IfanUr/WebprogrammerwroteadatabasequerythatextracteddataofatypetheJavaScriptwasn'texpecting,oriftheJavaScriptgeneratedanoutputofatypethattheXMLpagewasn'texpecting,pilerwouldregisterthediscrepancyandflagthecodeascontaininganerror. Often,codethatisn'texplicitlytypedstillhasimplicitconsistencyrules.Forinstance,ifyouwriteaqueryintheSQLdatabaselanguagethatasksfortheaveragenumericalvalueofabunchoftextfields,thedatabaseserverwilltellyouthatitcan'tprocessyourrequest.ToenableUr/WebtocoordinatetheflowofdatabetweenWebtechnologies,ChlipalahadtocreatelibrariesofnewdatatypesforSQL,XML,andcascadingstylesheets(CSS)thatembodytheserules. WhiletheUr/pilerdoesgenerateXML,JavaScript,andSQLcodeinitscurrentversion,itdoesn'tproducestylesheetsautomatically.But,Chlipalasays,"Onethingpilercandoisanalyzeyourfullprogramandsay,'HereisanexhaustivelistofalltheCSSclassesthatmightbementioned,andhereisadescriptionofthecontextinwhicheachclassmightbeused,whichtellsyouwhatpropertiesmightbeworthsetting.'So,forinstance,someparticularclassmightneverbe 2/3 APAcitation:NewprogramminglanguageautomaticallycoordinatesinteractionsbetweenWebponents(2014,December23)retrieved22May2022from/news/2014-12-languageautomatically-interactions-web-page.html Thisdocumentissubjecttocopyright.Apartfromanyfairdealingforthepurposeofprivatestudyorresearch,nopartmaybereproducedwithoutthewrittenpermission.Thecontentisprovidedforinformationpurposesonly. PoweredbyTCPDF() 3/3