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Toward a Process Model for GI Service Composition

Toward a Process Model for GI Service Composition. Udo Einspanier, Michael Lutz, Ingo Simonis, Kristian Senkler, Adam Sliwinski Münsteraner GI-Tage 26-27 June 2003, Münster. Overview. Motivation OGC and ISO RM-ODP State of the art in Web Service Composition XPDL BPEL4WS DAML-S

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Toward a Process Model for GI Service Composition

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  1. Toward a Process Model for GI Service Composition Udo Einspanier, Michael Lutz, Ingo Simonis, Kristian Senkler, Adam Sliwinski Münsteraner GI-Tage 26-27 June 2003, Münster U. Einspanier, M. Lutz, I. Simonis, K. Senkler, A. Sliwinski

  2. Overview • Motivation • OGC and ISO RM-ODP • State of the art in Web Service Composition • XPDL • BPEL4WS • DAML-S • Comparison & Conclusion U. Einspanier, M. Lutz, I. Simonis, K. Senkler, A. Sliwinski

  3. Motivation • Composability greatest value of (GI) web services  Service Composition is a „hot topic“ • Concepts for GI service composition have several deficits, but... ... there are a number of approaches outside the GI domain • Goal: Compare these approaches to OGC/ISO approach and point out possible connections U. Einspanier, M. Lutz, I. Simonis, K. Senkler, A. Sliwinski

  4. ISO RM-ODP • Specifies: • concepts and framework for the description of distributed systems • characteristics that qualify a distributed system as “open” • Objective: development of standards that allow distributed services in a heterogeneous environment • Division of an ODP system into 5 viewpoints U. Einspanier, M. Lutz, I. Simonis, K. Senkler, A. Sliwinski

  5. ISO RM-ODP Viewpoints U. Einspanier, M. Lutz, I. Simonis, K. Senkler, A. Sliwinski

  6. OpenGIS and ISO 19100 • RM-ODP only provides the „big picture“ • Specification of geospatial processing components is the objective of OGC & ISO 19100 • concepts • service • interface • operation • service chain • workflow U. Einspanier, M. Lutz, I. Simonis, K. Senkler, A. Sliwinski

  7. 3 types of service chaining • User defined (transparent) chaining • Workflow-managed (translucent) chaining • Aggregate service (opaque chaining) U. Einspanier, M. Lutz, I. Simonis, K. Senkler, A. Sliwinski

  8. Limitations • No uniform model to integrate web services into higher level architectures or business processes • No descriptive language to define a chain and rules or execution constraints • Only weak approaches to ensure „semantic interoperability“ U. Einspanier, M. Lutz, I. Simonis, K. Senkler, A. Sliwinski

  9. XML Based Process Definition Language (XPDL) • XPDL is a graph-structured process definition language • XPDL describes a process definition in terms of • what is to be done, • when it has to be done, • under what conditions, and • by whom or what • ‘activity’ is the key concept of an XPDL process definition U. Einspanier, M. Lutz, I. Simonis, K. Senkler, A. Sliwinski

  10. XPDL – Language Details U. Einspanier, M. Lutz, I. Simonis, K. Senkler, A. Sliwinski

  11. What about Web Services? • An external reference can be defined that points to an application, e. g. a web service • Mature metamodel • Lacks crucial concepts for building processes on web service architectures U. Einspanier, M. Lutz, I. Simonis, K. Senkler, A. Sliwinski

  12. BPEL4WS a.k.a BPEL • XML-based process definition languagereleased by IBM, Microsoft and BEA • supersedes process definition languages XLANG and WSFL • models the behaviour of web services in a business process interaction U. Einspanier, M. Lutz, I. Simonis, K. Senkler, A. Sliwinski

  13. BPEL Concepts • BPEL builds on top of WSDL „stateful extension“ • BPEL supports two kinds of business processes: • Business protocols specify the mutually visible message exchange behaviour without revealing internal behaviour. • Executable business processes model actual behaviour of participant in a business interaction. U. Einspanier, M. Lutz, I. Simonis, K. Senkler, A. Sliwinski

  14. BPEL – Language Details • A BPEL process has three main parts: • partners (i.e. either a service the process invokes or those that invoke the process), • activities (i.e. an operation in a business process), • containers (provide means to store messages that constitute the state of the business process). U. Einspanier, M. Lutz, I. Simonis, K. Senkler, A. Sliwinski

  15. BPEL – Information Flow • Control flow is handled via “service links”: • interaction with each partner occurs through web service interfaces; • the structure of the relationship at the interface level is encapsulated in service links. • Data flow is handled by containers. • Message flow is handled by three types of activities: receive,reply,invoke U. Einspanier, M. Lutz, I. Simonis, K. Senkler, A. Sliwinski

  16. DAML-based Web Service Ontology (DAML-S) • Both an ontology of and language for describing services • Goal: Enable automatic invocation, execution monitoring, discovery and composition of web services • Service description consists of • service profile  what it requires/provides • service model  how it works • service grounding  how it can be accessed U. Einspanier, M. Lutz, I. Simonis, K. Senkler, A. Sliwinski

  17. Process input hasProfile Profile precondition hasProcess conditional output conditional effect Composite Process computedInput Atomic Simple computedOutput Process realizes collapse Process computedEffect realizedBy expand hasGrounding computedPrecondition invocable DAML-S – Language Details • atomic processescan be directlyinvoked (WSDLgrounding) • composite processescan be decomposedinto other processes • simple processes are used as views on atomic or composite processes for planning and reasoning U. Einspanier, M. Lutz, I. Simonis, K. Senkler, A. Sliwinski

  18. Comparison of Concepts of OGC and ISO RM-ODP • necessary for integration into OGC/ISO architecture • lexical comparison • based on core concepts • XPDL: workflow process activity, transition information, workflow process definition • BPEL: process, activity • DAML-S: simple, composite and atomic process U. Einspanier, M. Lutz, I. Simonis, K. Senkler, A. Sliwinski

  19. Comparison – a first approximation U. Einspanier, M. Lutz, I. Simonis, K. Senkler, A. Sliwinski

  20. Conclusions & Future Research • OGC work currently lacks crucial concepts that facilitate service composition • There are approaches outside the GI domain that could compensate these limitations (e.g. XPDL, BPEL, DAML-S) • A Comparison of concepts used in these approaches to those used by OGC is vital, but difficult • Comparison has to be improved • go beyond entity level  properties and relationships • take viewpoint-specific concepts intoaccount U. Einspanier, M. Lutz, I. Simonis, K. Senkler, A. Sliwinski

  21. Thank you! Questions? • http://www.meanings.de • X-Border • DALI U. Einspanier, M. Lutz, I. Simonis, K. Senkler, A. Sliwinski

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