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The Dynamic Discovery of Web Services Using WSMX

The Dynamic Discovery of Web Services Using WSMX. Presented by Robert Zaremba. Requirements of Web Services in the B2B Domain. Discovery Web Service directories are not machine-understandable Interoperability Differences in communication patterns that must be solved on the semantic level

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The Dynamic Discovery of Web Services Using WSMX

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  1. The Dynamic Discovery of Web Services Using WSMX Presented by Robert Zaremba

  2. Requirements of Web Services in the B2B Domain • Discovery • Web Service directories are not machine-understandable • Interoperability • Differences in communication patterns that must be solved on the semantic level • Composition • Current Web Service composition languages cannot bind services dynamically • Security and Reliability • The complex interactions introduced by a reliance on Web Services introduces security concerns

  3. Web Service Modeling Ontology (WSMO) • Developed by the ESSI WSMO working group • Aims to enable the partial automation of the registration, discovery, and execution of Web Services • Incorporates semantic mark-up into all aspects of Web Services • Has its conceptual basis in the Web Service Modeling Framework (WSMF)

  4. WSMO Design Goals • Web Compliance • Ontology-Based • Strict Decoupling • Centrality of Mediation • Ontological Role Separation • Description versus Implementation • Execution Semantics • Service versus Web Service

  5. Top-Level Elements of WSMO • Ontologies • Terminology used to describe the relevant domains to the WSMO elements • Web Services • Computational entities which provide a service that has value in the domain • Goals • The functionality that is desired by the user • Mediators • Handles various interoperability problems between elements

  6. Web Service Modeling Language (WSML) • Developed by the ESSI WSML working group, which is a part of the ESSI WSMO working group • Is a formalization of WSMO • Has several variants with different levels of logical expressiveness • Provides a framework to describe semantic Web Services • Avoids complex logical expressions • Adopts namespace and datatype concepts from XML

  7. WSML - Ontologies • Ontologies may be imported • Mediators resolve mismatches between imported ontologies • Concepts are the basic elements from the problem domain • Relations model interdependencies between concepts • Functions allow for transformations of data • Instances need not be specified; may link to an external store • Axioms are logical expressions together with non-functional properties

  8. Example of a WSML Ontology 1wsmlVariant _"http://www.wsmo.org/wsml/wsml-syntax/wsml-flight" 2 3namespace {_"http://www.example.org/Family#", 4 dc _"http://purl.org/dc/elements/1.1#"} 5 6ontology Family 7concept Human 8hasParentinverseOf(hasChild) ofType Human 9hasChildofType Human 10hasAgeInYearsofType (0 1) _integer 11 12axiomDefinitionTeenager 13nonFunctionalProperties 14dc#sourcehasValue _"http://dictionary.reference.com/search?q=teenager" 15endNonFunctionalProperties 16definedBy 17forall {?teen,?age} ( 18 ?teen memberOf Teenager impliedBy 19 ?teen[hasAgeInYearshasValue ?age] memberOf Human and 20 ?age >= 13 and ?age =< 19).

  9. WSML – Web Services • NonFunctionalProperties include QoS, Accuracy, Owner, etc. • Ontologies are imported to provide the vocabulary of the Web Service specification • ooMediators can be used to resolve conflicts between imported Ontologies • wwMediators resolve incompatibilities when interacting with other Web Services • Capability describes the functionality provided by the Web Service including necessary preconditions, assumptions, postconditions, and effects • Interface describes the choreography and orchestration of the Web Service

  10. WSML - Goals • Ontologies may be imported • ooMediators are used to resolve conflicts in imported Ontologies • ggMediators allow for the reuse and refinement of an existing goal • Capability describes the requested functionality

  11. An Example Goal

  12. WSML - Mediators • Ontologies may be imported • Source specifies the WSMO element that will be transformed • Target is the WSMO element that receives the mediated element • A mediation service is a service that will provide the mapping

  13. Web Service Execution Environment (WSMX) • Developed by DERI International under SDK cluster • Is a reference implementation of WSMO • An implementation is available from http://www.wsmx.org/ • Implemented in Java • Runs its own micro-kernel • Provides a HTTP GUI as well as support for SSH • Exposes Mbean interfaces for the management of components • Currently lacks documentation

  14. WSMX Architecture • Components have well-defined interfaces • Components may be separated by network(s) • Communication is event-based

  15. Adapter • Outside of WSMX • Transforms incoming messages to WSMX format • Handles mismatches on the communication layer

  16. Compiler • Validates WSML documents • Used in all operations

  17. Matchmaker • Matches Web Services to Goals • Input: set of registered Web Services and the requester’s Goal • Output: set of Web Services that match the Goal

  18. Data Mediator • Maps source ontology to target ontology • Based on ooMediator from the WSMO specification • Provides design-time component for analyzing ontologies and creating mappings for run-time use

  19. Choreography Engine • Uses Mediators to compensate for communication pattern mismatches • Generates dummy acknowledgement messages and can group and reorder messages • Choreography rules are created at design-time and stored

  20. Communication Manager • Handles invocations from requesters • Invoke Web Services and retrieve the results back to WSMX • Data needed for invocation must be in XML format

  21. Other Components • WSMX Manager coordinates the other components • Resource Manager provides access to the persistence components • Composition component will handle complex service compositions • Security component will handle security aspects

  22. Web Service Registration • The WSML description of the Web Service is defined in the editor • The Communication Manager handles the actual invocation • The Compiler checks the syntax of the WSML document • The WSML document is added to the repository

  23. Web Service Discovery • The Adapter converts the request into a WSML Goal • The Communication Manager receives the invocation • The Compiler checks the syntax of the WSML document • The Matchmaker selects Web Services that match the Goal, using the Data Mediator if necessary

  24. Web Service Invocation • The requestor specifies the Web Service and provides an Ontology instance, not necessarily in WSML format • The Adapter ensures that the request is in WSML format • The requester’s Communication Manager sends the Ontology instance and Web Service to the Choreography Engine and Compiler • The Choreography Engine mediates the communication between the Communication Managers while the Compiler verifies that the documents are syntactically correct • The provider’s Communication Manager converts the required data into XML format, using the Data Mediator when necessary • The service provider provides the service, returning data if necessary either synchronously or asynchronously

  25. My Impressions • WSML is easy to understand and use • HTTP GUI simplifies the management of the components • It incorporates support for Apache’s Axis, a popular free Web Service design and deployment platform • Requires an understanding of J2EE’s Java Management Extensions (JMX) • The lack of documentation is a problem

  26. Sources • A. Haller, E. Cimpian, A. Mocan, E. Oren, C. Bussler: WSMX - A Semantic Service-Oriented Architecture, in Proceedings of the International Conference on Web Service (ICWS 2005). Orlando, Florida, 2005. • M. Zaremba, C. Bussler: Towards Dynamic Execution Semantics in Semantic Web Services, In Proceedings of the Workshop on Web Service Semantics: Towards Dynamic Business Integration, International Conference on the World Wide Web (WWW2005). Chiba, Japan, 2005. • Dumitru Roman, Uwe Keller, Holger Lausen, Jos de Bruijn, Rub�n Lara, Michael Stollberg, Axel Polleres, Cristina Feier, Christoph Bussler, and Dieter Fensel: Web Service Modeling Ontology, Applied Ontology, 1(1): 77 - 106, 2005. • K. Verma, A. Mocan, M. Zaremba, A. Sheth, J. A. Miller: Linking Semantic Web Service Efforts, In Proceedings of the ICWS 2005 Second International Workshop on Semantic and Dynamic Web Processes (SDWP 2005). Orlando, Florida, 2005. • D16.1v0.21 The Web Service Modeling Language WSML. Retrieved on March 22, 2007 from http://www.wsmo.org/TR/d16/d16.1/v0.21/#cha:wsml-basic-syntax

  27. Questions?

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