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

26 June 2003U. 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

26 June 2003U. 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

26 June 2003U. 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

26 June 2003U. Einspanier, M. Lutz, I. Simonis, K. Senkler, A. Sliwinski 5 ISO RM-ODP Viewpoints

26 June 2003U. Einspanier, M. Lutz, I. Simonis, K. Senkler, A. Sliwinski 6 OpenGIS and ISO RM-ODP only provides the „big picture“ Specification of geospatial processing components is the objective of OGC & ISO concepts  service  interface  operation  service chain  workflow

26 June 2003U. 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)

26 June 2003U. 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“

26 June 2003U. 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

26 June 2003U. Einspanier, M. Lutz, I. Simonis, K. Senkler, A. Sliwinski 10 XPDL – Language Details

26 June 2003U. 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

26 June 2003U. Einspanier, M. Lutz, I. Simonis, K. Senkler, A. Sliwinski 12 BPEL4WS a.k.a BPEL XML-based process definition language released by IBM, Microsoft and BEA supersedes process definition languages XLANG and WSFL models the behaviour of web services in a business process interaction

26 June 2003U. 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.

26 June 2003U. 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).

26 June 2003U. 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

26 June 2003U. 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

26 June 2003U. Einspanier, M. Lutz, I. Simonis, K. Senkler, A. Sliwinski 17 DAML-S – Language Details Process input precondition conditional output conditional effect Profile hasProfile hasProcess Atomic Process hasGrounding Simple Process realizedBy realizes Composite Process computedInput computedOutput computedEffect computedPrecondition invocable expand collapse atomic processes can be directly invoked (WSDL grounding) composite processes can be decomposed into other processes simple processes are used as views on atomic or composite processes for planning and reasoning

26 June 2003U. 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

26 June 2003U. Einspanier, M. Lutz, I. Simonis, K. Senkler, A. Sliwinski 19 Comparison – a first approximation RM-ODPOGC XPDL workflow process activityactivityoperation transition informationactiontransformation workflow process definition?workflow BPEL processchain of actionstranslucent / opaque service chain activityaction– DAML-S simple processactivityopaque service chain composite processchain of actionsservice chain atomic processactivityoperation

26 June 2003U. 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 into account

26 June 2003U. Einspanier, M. Lutz, I. Simonis, K. Senkler, A. Sliwinski 21 Thank you! Questions? X-Border DALI