Diploma Thesis DIP-2822

BibliographySonntag, Mirko: Conceptual Design and Implementation of a BPEL light Workflow Engine With Support for Message Exchange Patterns..
University of Stuttgart, Faculty of Computer Science, Electrical Engineering, and Information Technology, Diploma Thesis No. 2822 (2008).
119 pages, english.
CR-SchemaH.4.1 (Office Automation)
K.1 (The Computer Industry)
D.2.12 (Software Engineering Interoperability)
C.3 (Special-Purpose and Application-Based Systems)
D.2.13 (Software Engineering Reusable Software)
KeywordsSOA; BPEL; BPEL light; ODE; Workflow; BPM

The Business Process Execution Language (BPEL) is the common standard for describing business processes being widely accepted by industry and research. These business processes can be seen as a composition of Web Services (also referred to as orchestration). BPEL’s communication is tightly coupled to WSDL 1.1: each BPEL basic interaction activity corresponds to a WSDL operation type; variables are related to WSDL messages, and so on. The coupling between BPEL and WSDL 1.1 brings some significant drawbacks. First, it prohibits a priori the usage of another interface definition language a user may want to take (e.g. SSDL). Second, modelling a BPEL business process presumes both, knowledge in business and IT level. To overcome these deficiencies BPELlight was invented, a BPEL 2.0 extension decoupling process logic from interface definitions. In short, it emulates all BPEL constructs that directly refer to WSDL elements. That way BPELlight facilitates the reusable and flexible modelling of business processes.

In WSDL 2.0 a Message Exchange Pattern (MEP) template was introduced. MEPs describe the communication between two or more parties and can go beyond simple one-way or request-response operations as opposed to WSDL 1.1 operations. The template can be compared to an orchestration language describing the message flow within an operation from the service’s point of view. But it lacks the solution of some issues of great importance that can be overcome by formalizing MEPs with BPELlight (e.g. machine readability, communication with several instances of a node). Therefore an abstract process profile was defined to enable the definition of reusable MEPs as abstract BPELlight processes.

This diploma thesis extends the first version of BPELlight to achieve two goals. First, the separation of BPEL and WSDL is pushed. Previously unregarded concepts are considered (e.g. event and fault handling). Second, the idea of defining MEPs with BPELlight is integrated into BPELlight process models as description of the interaction activity’s behaviour. On the one hand this enables an interaction activity to express an arbitrary complex message exchange. On the other hand it facilitates a recursive definition of MEPs.

The introduced concepts are proven by the specification and prototypical implementation of a BPELlight workflow engine on basis of Apache ODE, a BPEL 2.0 workflow machine. The prototype allows binding BPELlight process models against WSDL 2.0 interfaces at deployment. The integration with an Axis 2 service bus makes it possible to publish process models and to communicate with eligible partners. BPELlight MEP processes, which describe the behaviour of interaction activities, are additionally used to carry out the specified behaviour at runtime. They are therefore parameterized during deployment and synchronously invoked when the appropriate interaction activity is executed.

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Department(s)University of Stuttgart, Institute of Architecture of Application Systems
Superviser(s)van Lessen, Tammo; Nitzsche, Jörg
Entry dateNovember 24, 2008
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