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UMBC CMSC 691 - Introduction to the Semantic Web

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Introduction to the Semantic WebQuestionsSlide 3Slide 4Slide 5IOHOOriginsW3C’s Semantic Web GoalsTBL’s semantic web visionWhy is this hard?What a web page looks like to a machine…OK, so HTML is not helpfulXML to the rescue?XML  machine accessible meaningXML Schema helpsBut there are many schemasThere’s no way to relate schemaAn Ontology level is neededToday and tomorrowThe Semantic Web WaveSemantic Web LanguagesSemantic web languages todayTwo Semantic Web NotionsRDF is the first SW languageThe RDF Data ModelURIs are a foundationWhat does a URI mean?The RDF GraphSimple RDF ExampleXML encoding for RDFN triple representationTriple NotesN3 notation for RDFN3 ExampleA usecase: FOAFFOAF VocabularyFOAF: why RDF? Extensibility!No free lunch!More RDF VocabularyRDF is being used!RDF Schema (RDFS)RDFS VocabularyRDF and RDF SchemaRDFS supports simple inferencesN3 exampleIs RDF(S) better than XML?From where will the markup come?Slide 49Problems with RDFSDAML+OIL = RDF + KRW3C’s Web Ontology Language (OWL)OWL  RDFOwl is based on Description LogicOWL Class ConstructorsOWL AxiomsOWL LanguageOWL Lite FeaturesOWL FeaturesOWL OntologiesOWL in One SlideIntroduction to theSemantic WebQuestions•What is the Semantic Web?•Why do we want it?•How will we do it?•Who will do it?•When will it be done?“XML is Lisp's bastard nephew, with uglier syntax and no semantics. Yet XML is poised to enable the creation of a Web of data that dwarfs anything since the Library at Alexandria.”-- Philip Wadler, Et tu XML? The fall of the relational empire, VLDB, Rome, September 2001.“The web has made people smarter. We need to understand how to use it to make machines smarter, too.” -- Michael I. Jordan, paraphrased from a talk at AAAI, July 2002 by Michael Jordan (UC Berkeley)“The Semantic Web will globalize KR, just as the WWW globalize hypertext” -- Tim Berners-LeeIOHO•The web is like a universal acid, eating through and consuming everything it touches.-Web principles and technologies are equally good for wireless/pervasive computing•The semantic web is our first serious attempt to provide semantics for XML sublanguages•It will provide mechanisms for people and machines (agents, programs, web services) to come together.-In all kinds of networked environments: wired, wireless, ad hoc, wearable, etc.OriginsTim Berners-Lee’s original 1989 WWW proposal described a web of relationships among namedobjects unifying many info. management tasks. Capsule history• Guha’s MCF (~94) • XML+MCF=>RDF (~96)• RDF+OO=>RDFS (~99)• RDFS+KR=>DAML+OIL (00)• W3C’s SW activity (01)• W3C’s OWL (03)http://www.w3.org/History/1989/proposal.htmlW3C’s Semantic Web GoalsFocus on machine consumption:"The Semantic Web is an extension of the current web in which information is given well-defined meaning, better enabling computers and people to work in cooperation." -- Berners-Lee, Hendler and Lassila, The Semantic Web, Scientific American, 2001TBL’s semantic web visionWhy is this hard?after Frank van Harmelenand Jim HendlerWhat a web page looks like to a machine…after Frank van Harmelenand Jim HendlerOK, so HTML is not helpfulMaybe we can tell the machine what the different parts of the text represent?titletimespeakerlocationabstractbiosketchhostXML to the rescue?XML fans propose creating a XML tag set to use for each application.For talks, we can choose <title>, <speaker>, etc.after Frank van Harmelen and Jim Hendler<title><time><speaker><location><abstract><biosketch><host> </host></biosketch></abstract></location></time></speaker></title>XML  machine accessible meaningBut, to your machine, the tags still look like this….The tag names carry no meaning.XML DTDs andSchemas have little or no semantics.after Frank van Harmelen and Jim Hendler<?xml version="1.0" encoding="utf-8"?> <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"> <xs:element name="book"> <xs:complexType> <xs:sequence> <xs:element name="title" type="xs:string"/> <xs:element name="author" type="xs:string"/> <xs:element name="character" minOccurs="0" maxOccurs="unbounded"> <xs:complexType> <xs:sequence> <xs:element name="name" type="xs:string"/> <xs:element name="friend-of" type="xs:string" minOccurs="0" maxOccurs="unbounded"/> <xs:element name="since" type="xs:date"/> <xs:element name="qualification" type="xs:string"/> </xs:sequence> </xs:complexType> </xs:element> </xs:sequence> <xs:attribute name="isbn" type="xs:string"/> </xs:complexType> </xs:element></xs:schema>XML Schema helpsXML Schemas provide a simple mechanism to define shared vocabularies.XML Schema fileafter Frank van Harmelen and Jim Hendler<?xml version="1.0" encoding="utf-8"?> <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"> <xs:element name="book"> <xs:complexType> <xs:sequence> <xs:element name="title" type="xs:string"/> <xs:element name="author" type="xs:string"/> <xs:element name="character" minOccurs="0" maxOccurs="unbounded"> <xs:complexType> <xs:sequence> <xs:element name="name" type="xs:string"/> <xs:element name="friend-of" type="xs:string" minOccurs="0" maxOccurs="unbounded"/>


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UMBC CMSC 691 - Introduction to the Semantic Web

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