csci5211: Computer Networks and Data Communications

Internet Engineering CourseSemantic Web,Web Services,Semantic Web Services

11AgendaVision of Next Generation Web Technology Semantic WebTodays WebThe Semantic Web ImpactSemantic Web TechnologiesA Layered Approach Web Services Why Web Services? Enabling Technologies Web Service Composition Main Issues concerning the composition Semantic Web Services

2Static500 million users more than 3 billion pagesWWWURI, HTML, HTTPVision of Next Generation Web Technologies3WWWURI, HTML, HTTPSerious Problems in information finding,information extracting,information representing,information interpreting andand information maintaining.Semantic WebRDF, RDF(S), OWLStaticVision of Next Generation Web Technologies4WWWURI, HTML, HTTPBringing the computer back as a device for computationSemantic WebRDF, RDF(S), OWLDynamicWeb ServicesUDDI, WSDL, SOAPStaticVision of Next Generation Web Technologies5WWWURI, HTML, HTTPBringing the web to its full potentialSemantic WebRDF, RDF(S), OWLDynamicWeb ServicesUDDI, WSDL, SOAPStaticSemantic WebServicesVision of Next Generation Web Technologies67

Semantic Web78Semantic Web OutlineTodays WebThe Semantic Web ImpactSemantic Web TechnologiesA Layered Approach9Todays WebMost of todays Web content is suitable for human consumption Even Web content that is generated automatically from databases is usually presented without the original structural information found in databases Typical Web uses today peoplesseeking and making use of information, searching for and getting in touch with other people, reviewing catalogues of online stores and ordering products by filling out forms10Keyword-Based Search Engines Current Web activities are not particularly well supported by software toolsExcept for keyword-based search engines (e.g. Google, AltaVista, Yahoo)The Web would not have been the huge success it was, were it not for search engines 11Problems of Keyword-Based Search EnginesHigh recall, low precision.Low or no recallResults are highly sensitive to vocabulary Results are single Web pages Human involvement is necessary to interpret and combine resultsResults of Web searches are not readily accessible by other software tools12The Key Problem of Todays WebThe meaning of Web content is not machine-accessible: lack of semantics It is simply difficult to distinguish the meaning between these two sentences:I am a professor of computer science.I am a professor of computer science, you may think. Well, . . .13The Semantic Web ApproachRepresent Web content in a form that is more easily machine-processable.Use intelligent techniques to take advantage of these representations. The Semantic Web will gradually evolve out of the existing Web, it is not a competition to the current WWW14Semantic Web OutlineTodays WebThe Semantic Web ImpactSemantic Web TechnologiesA Layered Approach15The Semantic Web Impact Knowledge ManagementKnowledge management concerns itself with acquiring, accessing, and maintaining knowledge within an organizationKey activity of large businesses: internal knowledge as an intellectual asset It is particularly important for international, geographically dispersed organizationsMost information is currently available in a weakly structured form (e.g. text, audio, video)

16Limitations of Current Knowledge Management TechnologiesSearching information Keyword-based search engines Extracting informationhuman involvement necessary for browsing, retrieving, interpreting, combiningMaintaining informationinconsistencies in terminology, outdated information.Viewing information Impossible to define views on Web knowledge 17Semantic Web Enabled Knowledge ManagementKnowledge will be organized in conceptual spaces according to its meaning.Automated tools for maintenance and knowledge discoverySemantic query answeringQuery answering over several documentsDefining who may view certain parts of information (even parts of documents) will be possible.18The Semantic Web Impact B2C Electronic CommmerceA typical scenario: user visits one or several online shops, browses their offers, selects and orders products. Ideally humans would visit all, or all major online stores; but too time consumingShopbots are a useful tool

19Limitations of ShopbotsThey rely on wrappers: extensive programming requiredWrappers need to be reprogrammed when an online store changes its outfitWrappers extract information based on textual analysisError-proneLimited information extracted

20Semantic Web Enabled B2C Electronic CommerceSoftware agents that can interpret the product information and the terms of service.Pricing and product information, delivery and privacy policies will be interpreted and compared to the user requirements.Information about the reputation of shops Sophisticated shopping agents will be able to conduct automated negotiations

21The Semantic Web Impact B2B Electronic CommerceGreatest economic promiseCurrently relies mostly on EDIIsolated technology, understood only by expertsDifficult to program and maintain, error-proneEach B2B communication requires separate programming Web appears to be perfect infrastructureBut B2B not well supported by Web standards22Semantic Web Enabled B2B Electronic CommerceBusinesses enter partnerships without much overhead Differences in terminology will be resolved using standard abstract domain modelsData will be interchanged using translation services. Auctioning, negotiations, and drafting contracts will be carried out automatically (or semi-automatically) by software agents23Semantic Web OutlineTodays WebThe Semantic Web ImpactSemantic Web TechnologiesA Layered Approach24Semantic Web TechnologiesExplicit MetadataOntologiesLogic and InferenceAgents25On HTMLWeb content is currently formatted for human readers rather than programsHTML is the predominant language in which Web pages are written (directly or using tools)Vocabulary describes presentation26An HTML ExampleAgilitas Physiotherapy CentreWelcome to the home page of the Agilitas Physiotherapy Centre. Do you feel pain? Have you had an injury? Let our staff Lisa Davenport,Kelly Townsend (our lovely secretary) and Steve Matthews take careof your body and soul.Consultation hoursMon 11am - 7pm
Tue 11am - 7pm
Wed 3pm - 7pm
Thu 11am - 7pm
Fri 11am - 3pmBut note that we do not offer consultation during the weeks of the State Of Origin games.

27Problems with HTMLHumans have no problem with thisMachines (software agents) do:How distinguish therapists from the secretary, How determine exact consultation hours They would have to follow the link to the State Of Origin games to find when they take place.28A Better Representation

PhysiotherapyAgilitas Physiotherapy CentreLisa DavenportSteve MatthewsKelly Townsend

29Explicit MetadataThis representation is far more easily processable by machinesMetadata: data about data Metadata capture part of the meaning of dataSemantic Web does not rely on text-based manipulation, but rather on machine-processable metadata 30OntologiesThe term ontology originates from philosophy The study of the nature of existenceDifferent meaning from computer scienceAn ontology is an explicit and formal specification of a conceptualization31Typical Components of OntologiesTerms denote important concepts (classes of objects) of the domain e.g. professors, staff, students, courses, departments Relationships between these terms: typically class hierarchiesa class C to be a subclass of another class C' if every object in C is also included in C' e.g. all professors are staff members

32Further Components of OntologiesProperties: e.g. X teaches YValue restrictions e.g. only faculty members can teach coursesDisjointness statements e.g. faculty and general staff are disjointLogical relationships between objects e.g. every department must include at least 10 faculty

Ontology ExampleConcept conceptual entity of the domain

Property attribte describing a concept

Relation relationship between concepts or properties

Axiom coherency description between Concepts / Properties / Relations via logical expressionsPersonStudentProfessorLectureisA hierarchy (taxonomy)nameemailFieldresearchfieldtopicSyllabusattendsholdsholds(Professor, Lecture) =>Lecture.topic = Professor.researchField34The Role of Ontologies on the WebOntologies provide a shared understanding of a domain: semantic interoperabilityovercome differences in terminology mappings between ontologiesOntologies are useful for the organization and navigation of Web sites

35The Role of Ontologies in Web SearchOntologies are useful for improving the accuracy of Web searches search engines can look for pages that refer to a precise concept in an ontology Web searches can exploit generalization/ specialization information If a query fails to find any relevant documents, the search engine may suggest to the user a more general query.If too many answers are retrieved, the search engine may suggest to the user some specializations.

36Web Ontology LanguagesRDF SchemaRDF is a data model for objects and relations between themRDF Schema is a vocabulary description language Describes properties and classes of RDF resourcesProvides semantics for generalization hierarchies of properties and classes

37Web Ontology Languages (2) OWL A richer ontology languagerelations between classes e.g., disjointnesscardinality e.g. exactly onericher typing of propertiescharacteristics of properties (e.g., symmetry)38Logic and InferenceLogic is the discipline that studies the principles of reasoningFormal languages for expressing knowledgeWell-understood formal semanticsDeclarative knowledge: we describe what holds without caring about how it can be deducedAutomated reasoners can deduce (infer) conclusions from the given knowledge 39An Inference Exampleprof(X) faculty(X)faculty(X) staff(X)prof(michael)We can deduce the following conclusions:faculty(michael)staff(michael)prof(X) staff(X)40Logic versus OntologiesThe previous example involves knowledge typically found in ontologiesLogic can be used to uncover ontological knowledge that is implicitly given It can also help uncover unexpected relationships and inconsistenciesLogic is more general than ontologiesIt can also be used by intelligent agents for making decisions and selecting courses of action 41Tradeoff between Expressive Power and Computational ComplexityThe more expressive a logic is, the more computationally expensive it becomes to draw conclusionsDrawing certain conclusions may become impossible if non-computability barriers are encountered. Our previous examples involved rules If conditions, then conclusion, and only finitely many objectsThis subset of logic is tractable and is supported by efficient reasoning tools 42Inference and ExplanationsExplanations: the series of inference steps can be retracedThey increase users confidence in Semantic Web agents: Oh yeah? button Activities between agents: create or validate proofs43Typical Explanation ProcedureFacts will typically be traced to some Web addresses The trust of the Web address will be verifiable by agentsRules may be a part of a shared commerce ontology or the policy of the online shop44Software AgentsSoftware agents work autonomously and proactively They evolved out of object oriented and compontent-based programmingA personal agent on the Semantic Web will:receive some tasks and preferences from the personseek information from Web sources, communicate with other agentscompare information about user requirements and preferences, make certain choicesgive answers to the user45Semantic Web Agent TechnologiesMetadata Identify and extract information from Web sourcesOntologiesWeb searches, interpret retrieved information Communicate with other agentsLogicProcess retrieved information, draw conclusions46Semantic Web Agent Technologies (2)Further technologies (orthogonal to the Semantic Web technologies)Agent communication languagesFormal representation of beliefs, desires, and intentions of agentsCreation and maintenance of user models. 47Semantic Web OutlineTodays WebThe Semantic Web ImpactSemantic Web TechnologiesA Layered Approach48A Layered ApproachThe development of the Semantic Web proceeds in stepsEach step building a layer on top of anotherPrinciples:Downward compatibility Upward partial understanding

49The Semantic Web Layer Tower

50Semantic Web LayersXML layerSyntactic basisRDF layerRDF basic data model for factsRDF Schema simple ontology languageOntology layerMore expressive languages than RDF SchemaCurrent Web standard: OWL

51Semantic Web Layers (2)Logic layer enhance ontology languages furtherapplication-specific declarative knowledge Proof layerProof generation, exchange, validationTrust layerDigital signaturesrecommendations, rating agencies .

Web Services52AgendaWhat are Web Services?Why Web Services?Enabling Technologies?What is Web Service Composition?Main Issues concerning the composition?53

Web Evolution

XMLProgrammabilityConnectivityHTMLPresentationTCP/IP

TechnologyInnovationFTP, E-mail, GopherWeb PagesBrowse the WebProgram the WebWeb Services54What are Web Services?Definition from W3C "Web Service is a software application identified by a URI, whose interfaces and bindings are capable of being defined, described, and discovered by XML artifacts and which supports direct interactions with other software applications using XML-based messages via internet-based protocols".55What are Web Services?Every component that works in a network, is modular is self-descriptive,provides services independent of platform and application,conforms to an open set of standards and follows a common structure for description and invocation.56Why Web ServicesInteroperability. Any WS can interact with any other WS. Ubiquity. Any device which supports HTTP + XML can host & access WS. Effortless entry in this concept. easily understood + free toolkits Industry Support. major vendors support surrounding technology. 57Web Services ArchitectureComponentsService ProvidersService BrokersService RequestorsOperationsPublish / UnpublishFindBind58

59Enabling technologiesThey encapsulate a set of standards that allow the developers to implement distributed applications. SOAP (Simple Object Access Protocol),XML messaging protocol for basic service interoperabilityWSDL (Web Service Description Language) Common grammar for describing services UDDI (Universal Description Discovery and Integration)infrastructure required to publish and discover services.60SOAPUniform way of passing XML-encoded data.performing RPCs over SMTP, FTP, TCP/IP, HTTPThe requestor sends a msg to the serviceThe service processes the msg.The service sends back a response.

The requestor has no knowledge of how the service is implemented.61 My Life and Work Henry Ford mailto:henryford@hotmail.com http://www.henryford.com Samuel Crowther Martin Luther King Rd Raleigh North Carolina SOAP Example62SOAP - RPCMust define an RPC protocolHow will types be transported (in XML) and how application represents them.RPC parts (object id, operation name, parameters)SOAP assumes a type system based on XML-schema.63SOAP Example - doGoogleSearch

00000000000000000000000000000000 my query 0 10 true false latin1 latin1

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