rfc3987.Internationalized Resource Identifiers (IR

NetworkWorkingGroupM.DuerstRequestforComments:3987W3CCategory:StandardsTrackM.SuignardMicrosoftCorporationJanuary2005InternationalizedResourceIdentifiers(IRIs)StatusofThisMemoThisdocumentspecifiesanInternetstandardstrackprotocolfortheInternetcommunity,andrequestsdiscussionandsuggestionsforimprovements.PleaserefertothecurrenteditionoftheInternetOfficialProtocolStandards(STD1)forthestandardizationstateandstatusofthisprotocol.Distributionofthismemoisunlimited.CopyrightNoticeCopyright(C)TheInternetSociety(2005).AbstractThisdocumentdefinesanewprotocolelement,theInternationalizedResourceIdentifier(IRI),asacomplementtotheUniformResourceIdentifier(URI).AnIRIisasequenceofcharactersfromtheUniversalCharacterSet(Unicode/ISO10646).AmappingfromIRIstoURIsisdefined,whichmeansthatIRIscanbeusedinsteadofURIs,whereappropriate,toidentifyresources.TheapproachofdefininganewprotocolelementwaschoseninsteadofextendingorchangingthedefinitionofURIs.Thiswasdoneinordertoallowacleardistinctionandtoavoidincompatibilitieswithexistingsoftware.GuidelinesareprovidedfortheuseanddeploymentofIRIsinvariousprotocols,formats,andsoftwarecomponentsthatcurrentlydealwithURIs.TableofContents1.Introduction.........................31.1.OverviewandMotivation................31.2.Applicability.....................31.3.Definitions......................41.4.Notation........................52.IRISyntax..........................62.1.SummaryofIRISyntax.................62.2.ABNFforIRIReferencesandIRIs............7Duerst&SuignardStandardsTrack[Page1]RFC3987InternationalizedResourceIdentifiersJanuary20053.RelationshipbetweenIRIsandURIs..............103.1.MappingofIRIstoURIs................103.2.ConvertingURIstoIRIs................143.2.1.Examples....................154.BidirectionalIRIsforRight-to-LeftLanguages........164.1.LogicalStorageandVisualPresentation........174.2.BidiIRIStructure...................184.3.InputofBidiIRIs...................194.4.Examples........................195.NormalizationandComparison.................215.1.Equivalence......................225.2.PreparationforComparison...............225.3.ComparisonLadder...................235.3.1.SimpleStringComparison............235.3.2.Syntax-BasedNormalization...........245.3.3.Scheme-BasedNormalization...........275.3.4.Protocol-BasedNormalization..........286.UseofIRIs.........................296.1.LimitationsonUCSCharactersAllowedinIRIs.....296.2.SoftwareInterfacesandProtocols...........296.3.FormatofURIsandIRIsinDocumentsandProtocols...306.4.UseofUTF-8forEncodingOriginalCharacters......306.5.RelativeIRIReferences................327.URI/IRIProcessingGuidelines(informative).........327.1.URI/IRISoftwareInterfaces..............327.2.URI/IRIEntry.....................337.3.URI/IRITransferbetweenApplications.........337.4.URI/IRIGeneration...................347.5.URI/IRISelection...................347.6.DisplayofURIs/IRIs..................357.7.InterpretationofURIsandIRIs............367.8.UpgradingStrategy...................368.SecurityConsiderations...................379.Acknowledgements.......................3910.References..........................4010.1.NormativeReferences..................4010.2.InformativeReferences.................41A.DesignAlternatives.....................44A.1.NewScheme(s).....................44A.2.CharacterEncodingsOtherThanUTF-8..........44A.3.NewEncodingConvention................44A.4.IndicatingCharacterEncodingsintheURI/IRI.....45Authors’Addresses........................45FullCopyrightStatement.....................46Duerst&SuignardStandardsTrack[Page2]RFC3987InternationalizedResourceIdentifiersJanuary20051.Introduction1.1.OverviewandMotivationAUniformResourceIdentifier(URI)isdefinedin[RFC3986]asasequenceofcharacterschosenfromalimitedsubsetoftherepertoireofUS-ASCII[ASCII]characters.ThecharactersinURIsarefrequentlyusedforrepresentingwordsofnaturallanguages.Thisusagehasmanyadvantages:SuchURIsareeasiertomemorize,easiertointerpret,easiertotranscribe,easiertocreate,andeasiertoguess.FormostlanguagesotherthanEnglish,however,thenaturalscriptusescharactersotherthanA-Z.Formanypeople,handlingLatincharactersisasdifficultashandlingthecharactersofotherscriptsisforthosewhouseonlytheLatinalphabet.Manylanguageswithnon-LatinscriptsaretranscribedwithLatinletters.ThesetranscriptionsarenowoftenusedinURIs,buttheyintroduceadditionalambiguities.Theinfrastructurefortheappropriatehandlingofcharactersfromlocalscriptsisnowwidelydeployedinlocalversionsofoperatingsystemandapplicationsoftware.Softwarethatcanhandleawidevarietyofscriptsandlanguagesatthesametimeisincreasinglycommon.Also,increasingnumbersofprotocolsandformatscancarryawiderangeofcharacters.ThisdocumentdefinesanewprotocolelementcalledInternationalizedResourceIdentifier(IRI)byextendingthesyntaxofURIstoamuchwiderrepertoireofcharacters.Italsodefinesinternationalizedversionscorrespondingtootherconstructsfrom[RFC3986],suchasURIreferences.ThesyntaxofIRIsisdefinedinsection2,andtherelationshipbetweenIRIsandURIsinsection3.UsingcharactersoutsideofA-ZinI