Introduction to Introduction to Semantic Web Semantic Web

Service ArchitectureService Architecture

► The vision of the Semantic Web The vision of the Semantic Web

► Ontologies as the basic building block Ontologies as the basic building block

► Semantic Web Service Architecture Semantic Web Service Architecture

► Phases of Semantic Web Services Phases of Semantic Web Services

Static

500 million users 500 million users more than 3 billion pagesmore than 3 billion pages

WWWURI, HTML, HTTP

The VisionThe Vision

WWWURI, HTML, HTTP

Serious Problems inSerious Problems in ► information finding,information finding,► information extracting,information extracting,► information representing,information representing,► information interpreting information interpreting

andand► and information and information

maintaining.maintaining.

Semantic WebRDF, RDF(S), OWL

Static

The VisionThe Vision

WWWURI, HTML, HTTP

Bringing the computer Bringing the computer back as a device for back as a device for computationcomputation

Semantic WebRDF, RDF(S), OWL

Dynamic Web ServicesUDDI, WSDL, SOAP

Static

The VisionThe Vision

WWWURI, HTML, HTTP

Bringing the web to its full potentialBringing the web to its full potential

Semantic WebRDF, RDF(S), OWL

Dynamic Web ServicesUDDI, WSDL, SOAP

Static

Semantic WebServices

The VisionThe Vision

Deficiencies of WS Deficiencies of WS TechnologyTechnology

► current technologies allow usage of Web current technologies allow usage of Web ServicesServices

► but:but: only syntactical information descriptions only syntactical information descriptions syntactic support for discovery, composition and executionsyntactic support for discovery, composition and execution=> Web Service usability, usage, and integration => Web Service usability, usage, and integration

needs to be inspected manually needs to be inspected manually no semantically marked up content / servicesno semantically marked up content / services no support for the Semantic Web no support for the Semantic Web

=> current Web Service Technology Stack failed => current Web Service Technology Stack failed to to realize the promise of Web Servicesrealize the promise of Web Services

Semantic Web Technology Semantic Web Technology

+ +

Web Service TechnologyWeb Service Technology

Semantic Web ServicesSemantic Web Services

=> Semantic Web Services as integrated solution for => Semantic Web Services as integrated solution for realizing the vision of the next generation of the Web realizing the vision of the next generation of the Web

• allow machine supported data interpretation• ontologies as data model

automated discovery, selection, composition, and web-based execution of services

SWSA: What is it about?SWSA: What is it about?

► SWSA (Semantic Web Services Initiative SWSA (Semantic Web Services Initiative Architecture) has created a set of architectural and Architecture) has created a set of architectural and protocol abstractions that serve as a foundation for protocol abstractions that serve as a foundation for Semantic Web service technologies.Semantic Web service technologies.

► This paper describes the protocols exchanged This paper describes the protocols exchanged between the interacting entities or agents that between the interacting entities or agents that interpret and reason with semantic descriptions in interpret and reason with semantic descriptions in the deployment of Semantic Web services.the deployment of Semantic Web services.

Terminologies UsedTerminologies Used

► Web Service - software system designed to Web Service - software system designed to support interoperable machine-to-machine support interoperable machine-to-machine interaction over a network. interaction over a network.

► Semantic Web Service - layer on top of the web Semantic Web Service - layer on top of the web service infrastructure to supply semantic service infrastructure to supply semantic meaning for web services.meaning for web services.

► Agent – software Agent – software

SWSA Architectural FrameworkSWSA Architectural Framework

► Addresses five classes of Semantic Web agent Addresses five classes of Semantic Web agent requirements:requirements:

1.1. Dynamic Service DiscoveryDynamic Service Discovery

2.2. Service EngagementService Engagement

3.3. Service process enactmentService process enactment

4.4. Community support servicesCommunity support services

5.5. Quality of serviceQuality of service

AssumptionsAssumptions

► Agents can access, interpret and communicate Agents can access, interpret and communicate using ontologiesusing ontologies

► Service providers publish semantic descriptions of Service providers publish semantic descriptions of service capabilities and interaction protocols..service capabilities and interaction protocols..

► Requesting agents delegate internal objectives as Requesting agents delegate internal objectives as requests to service providers.requests to service providers.

Phases of Semantic Web Phases of Semantic Web ServiceService

InteractionInteraction►Candidate service discoveryCandidate service discovery►Service engagementService engagement►Service enactmentService enactment

Service interaction process.

Service DiscoveryService Discovery

► Process of identifying candidate services by clients to Process of identifying candidate services by clients to achieve their objectives.achieve their objectives.

► Stakeholders:Stakeholders: Service providers, use published protocolService providers, use published protocol Service requestors, use query protocolService requestors, use query protocol Matchmakers Matchmakers

► Service discovery requirements: Service discovery requirements: Language requirementsLanguage requirements Functional requirementsFunctional requirements Architectural requirementsArchitectural requirements

Language requirementsLanguage requirements

► For expressing capabilities and goalsFor expressing capabilities and goals Services’ characteristics and constraintsServices’ characteristics and constraints Message semantics (protocol during interaction)Message semantics (protocol during interaction) Requester requirements (goal, quality, security Requester requirements (goal, quality, security

and privacy)and privacy)

Functional RequirementsFunctional Requirements

► What are the task for each entity ?What are the task for each entity ? Providers must describe the capabilities and constraints on Providers must describe the capabilities and constraints on

offered servicesoffered services Requestors must create abstract characterizations of Requestors must create abstract characterizations of

required services to facilitate matching with published required services to facilitate matching with published capabilities.capabilities.

Requestors must locate and interact with peers or Requestors must locate and interact with peers or matchmakers that can respond to queries for matchmakers that can respond to queries for advertised advertised service descriptionsservice descriptions..

Matchmakers must compare descriptions of queries and Matchmakers must compare descriptions of queries and capabilities.capabilities.

Requestors must decide if they can satisfy the Requestors must decide if they can satisfy the preconditions specified in a prospective service’s self-preconditions specified in a prospective service’s self-description in order to use it.description in order to use it.

Architectural requirementArchitectural requirement

advertising protocolsadvertising protocols used by service providers used by service providers candidate service-discovery protocolscandidate service-discovery protocols used by used by

requestorsrequestors

Why needed?Why needed? Identify the various classes of agents for final resultIdentify the various classes of agents for final result

Service EngagementService Engagement

► Initial phase of interaction between requestor and Initial phase of interaction between requestor and potential provider.potential provider.

► Results in an agreement.Results in an agreement.► Service engagement requirements: Service engagement requirements:

Functional requirementsFunctional requirementso Service request FormulationService request Formulationo Contract preliminariesContract preliminarieso Contract NegotiationContract Negotiationo AgreementAgreement

Architectural requirementsArchitectural requirementso Negotiation protocolsNegotiation protocolso Negotiation servicesNegotiation serviceso Auditing servicesAuditing services

Engagement message Engagement message semanticssemantics

Negotiation ProtocolsNegotiation Protocols

► FIPA query-reply protocol (equivalent to)FIPA query-reply protocol (equivalent to)► Agree with no acknowledgement andAgree with no acknowledgement and► No negotiationNo negotiation

► FIPA request protocol (equivalent to)FIPA request protocol (equivalent to)► Agree or refuseAgree or refuse► No negotiationNo negotiation► But commitment to provide a serviceBut commitment to provide a service

► negotiate-commitmentnegotiate-commitment► A formal negotiationsA formal negotiations► No party left hangingNo party left hanging► Shared acknowledgement of a contract or commitment Shared acknowledgement of a contract or commitment

between thembetween them

Negotiate – Commitment Negotiate – Commitment ProtocolProtocol

Service EnactmentService Enactment

► Service is ready to be initiated.Service is ready to be initiated.► Requestor determines the information necessary to request Requestor determines the information necessary to request

performance of service and appropriate reaction to service performance of service and appropriate reaction to service success or failure.success or failure.

► Service enactment requirements: Service enactment requirements: Functional requirementsFunctional requirements

o Response interpretationResponse interpretationo Response translationResponse translationo Process mediation and delegationProcess mediation and delegationo etcetc

Architectural requirementsArchitectural requirementso Process mediation servicesProcess mediation serviceso Process scheduling and composition servicesProcess scheduling and composition serviceso Process execution and status logging servicesProcess execution and status logging serviceso Policy monitoring servicesPolicy monitoring services

► Three types enactment protocolsThree types enactment protocols One assume synchronous communicationOne assume synchronous communication Other two assume asynchronous communicationOther two assume asynchronous communication

Enactment ProtocolsEnactment Protocols

Community support servicesCommunity support services

► Another class of infrastructure services needed to Another class of infrastructure services needed to support communally maintained semantic web support communally maintained semantic web service activities. Need Services forservice activities. Need Services for Authenticated definitions and mappings among concepts Authenticated definitions and mappings among concepts

(ontology) and their derivatives.(ontology) and their derivatives. information and access security, privacy, and information and access security, privacy, and

confidentiality management.confidentiality management. community-based preference and reliability reporting community-based preference and reliability reporting

based on collected feedback from service clients.based on collected feedback from service clients. policy and protocol management as well as validation policy and protocol management as well as validation

and dispute resolution. and dispute resolution. lifecycle management.lifecycle management.

Quality of ServiceQuality of Service

► Enforcement of QoS metricsEnforcement of QoS metrics Can be topic of negotiation processes, Can be topic of negotiation processes, must be monitored during enactment;must be monitored during enactment;

► Enforcement of QoS-level agreements, Enforcement of QoS-level agreements, deadlines, accuracy, and cost.deadlines, accuracy, and cost.

► Currently under studyCurrently under study► Not addressed in detail by SWSA committee.Not addressed in detail by SWSA committee.

ReferencesReferences

► Mark Burstein, Christoph Bussler, Michal Zaremba, Tim Finin, Michael N.Huhns, Massimo Paolucci, Amit P. Sheth, Stuart Williams, “ A Semantic Web Services Architecture”, IEEE Internet Computing, September-October, 2005