A Mediated Approach towards Web Service Choreography

1. A Mediated Approach towards Web Service Choreography Michael Stollberg, Dumitru Roman, Juan Miguel Gomez DERI – Digital Enterprise Research Institute {first.last}@deri.org Semantic Web Services: Preparing to Meet the World of Business Applications (ISWC 2004 Workshop)

2. Problem Setting • promise of Web Services as “next generation EAI technology” • a functionality for integrating something • can be arbitrarily combined • have a seamless usage interface • semantic technologies allow more sophisticated support for this than the current Web Service tech stack => what is needed and how shall it work ? WSMO A Mediated Approach towards Web Service Choreography

3. Overview – what we aim at • The Choreography of a Web Service defines its usage interface • A Global Model defines how several Web Service interact to achieve a common business goal • Usage of Mediators to resolve possibly occurring mismatches between the Choreographies of Web Services participating in a Global Model • A Semantic Web Service solution for the Web Service promise WSMO A Mediated Approach towards Web Service Choreography

4. WS WS WS WSMO Web Service Description • complete item description • quality aspects • Web Service Management • Advertising of Web Service • Support for WS Discovery Capability functional description Non-functional Properties Core + WS-specific • Realization of WS by using • other Web Services • Functional • decomposition • WS • Composition Web Service Implementation (not of interest in Web Service Description) • Interaction Interface • for consuming WS • Messages • External Visible • Behavior • ‘Grounding’ Orchestration Choreography --- Interfaces --- WSMO A Mediated Approach towards Web Service Choreography

5. Choreography in WSMO “Interface of Web Service for client-service interaction when consuming the Web Service” Aspects: 1) Choreography: Interaction Interface of a Web Service 2) Global Model: multiple Web Services collaboration 3) Choreography Mediation: establish valid Choreographies WSMO A Mediated Approach towards Web Service Choreography

6. under construction Choreography Aspects External Visible Behavior • those aspects of the workflow of a Web Service where User Interaction is required • described by process / workflow constructs Communication Structure • messages sent and received • their order (messages are related to activities) Choreography Grounding • concrete communication technology for interaction • choreography related errors (e.g. input wrong, message timeout, etc.) related to WS behavior descriptions, e.g. WSCI, BPEL4WS WSMO A Mediated Approach towards Web Service Choreography

7. under construction Choreography Formal Model • Formalization needed to allow operations / mediation on WSMO Choreography Interfaces • Formal Basis: Abstract State Machines (ASM) • ASM consists of Constants and Transition Rules; all Transition Rules are executed simultaneously according to conditions • Generic, expressive technology to model behavior • Overcome the ‘Frame Problem’ • Usage: • A general ASM defines the formal semantics of the WSMO Choreography Description Language • Choreography Specifications are mapped into ASM representation to allow protocol level mediation operations WSMO A Mediated Approach towards Web Service Choreography

8. under construction Global Model Aspects • Definition a multi-participant contract that describes from a global viewpoint the common observable behavior of the collaborating WS participants (this is the definition of “choreography” from the W3C WS Choreography working group) • Main Description Notions • collaboration participants • information interchanged • information-driven interaction rules (channel, workunit,…) this is basically what WS CDL is about WSMO A Mediated Approach towards Web Service Choreography

9. Heterogeneity … Mismatches on structural / semantic / conceptual / level Occur between different components that shall interoperate Especially in distributed & open environments like the Internet Concept of Mediation (Wiederhold, 94): Mediators as components that resolve mismatches Declarative Approach: Semantic description of resources ‘Intelligent’ mechanisms that resolve mismatches independent of content Mediation cannot be fully automated (integration decision) Levels of Mediation within Semantic Web Services (WSMF): Data Level: mediate heterogeneous Data Sources Protocol Level: mediate heterogeneous Communication Patterns Process Level: mediate heterogeneous Business Processes Mediation Aspects WSMO A Mediated Approach towards Web Service Choreography

10. WSMO Mediators Structure Source Component WSMO Mediator uses a Mediation Service via 1 Target Component 1 .. n Source Component • as a Goal • directly • optionally incl. Mediation under construction: Semantic Mediation Techniques for all levels Mediation Services WSMO A Mediated Approach towards Web Service Choreography

11. if we have all this … WS 3 C 4. M 5 C WS 2 1. M 1 C WS 1 2. 3. M 17 C WS n mediated collaboration of multiple Semantic Web Service WSMO A Mediated Approach towards Web Service Choreography

12. What we have so far … WSMO supports this idea by its design general approach seems to be fitting Especially in distributed & open environments like the Internet What we are currently working on … WSMO Choreography General Approach Formal Model WSMO Mediators – general specification EU-IP proposal that targets these issues Future Issues Global Models / relation to Choreography Mediation techniques for data, protocol, and business mediation level Status & Outlook WSMO A Mediated Approach towards Web Service Choreography