Axel Martens

Analyzing web service based business processes

This paper is concerned with the application of Web services to distributed, cross-organizational business processes. In this scenario, it is crucial to answer the following questions: Do two Web services fit together in a way such that the composed system is deadlock-free? – the question of compatibility. Can one Web service be replaced by another while the remaining components stay untouched? – the question of equivalence. Can we reason about the soundness of one given Web service without considering the actual environment it will by used in? This paper defines the notion of usability – an intuitive and locally provable soundness criterion for a given Web services. Based on this notion, this paper demonstrates how the other questions could be answered. The presented method is based on Petri nets, because this formalism is widely used for modeling and analyzing business processes. Due to the existing Petri net semantics for BPEL4WS – a language that is in the very act of becoming the industrial standard for Web service based business processes – the results are directly applicable to real world examples.

Inter-operability of Workflow Applications: Local Criteria for Global Soundness

Automatic analysis techniques for business processes are crucial for todays workflow applications. Since business processes are rapidly changing, only fully automatic techniques can detect processes which might cause deadlocks or congestion. Analyzing a complete workflow application, however, is much too complex to be performed fully automatically. Therefore, techniques for analyzing single processes in isolation and corresponding soundness criteria have been proposed. Though these techniques may detect errors such as deadlocks or congestion, problems arising from an incorrect inter-operation with other processes are completely ignored. The situation becomes even worse for cross-organizational workflow applications, where some processes are not even available for analysis due to confidentiality reasons. We propose a technique which allows to detect but a few errors of workflow applications which arise from incorrect inter-operation of workflows. To this end, the dynamics of the inter-operation of different workflows must be specified by the help of sequence diagrams. Then, each single workflow can be checked for local soundness with respect to this specification. If each single workflow is locally sound, a composition theorem guarantees global soundness of the complete workflow application. This way, each organization can check its own workflows without knowing the workflows of other organizations--still global soundness is guaranteed.

Modeling and Model Checking Web Services

We give an overview on web services and the web service technology stack. We then show how to build Petri net models of web services formulated in the specification language BPEL4WS. We define an abstract correctness criterion for these models and study the automated verification according to this criterion. Finally, we relate correctness of web service models to the model checking problem for alternating temporal logics.

Business Provenance --- A Technology to Increase Traceability of End-to-End Operations

Todays enterprise applications span multiple systems and organizations, integrating legacy and newly developed software components to deliver value to business operations. Often business processes rely on human activities that may not be predicted in advance, and information exchange is heavily based on e-mails or attachments where the content is unstructured and needs discovery. Visibility of such end-to-end operations is required to manage compliance and business performance. Hence, it becomes necessary to develop techniques for tracking and correlating the relevant aspects of business operations as needed without the cost and overhead of a fully fledged data and process reengineering. Our business provenance solution provides a generic data model and middleware infrastructure to collect and correlate information about how data was produced, what resources were involved and which tasks were executed. Business provenance gives the flexibility to selectively capture information required to address a specific compliance or performance goal. Additionally, a powerful correlation mechanism yields a representation of the end-to-end operation that puts each business artifact into the right context, for example, to detect situations of compliance violations and find their root causes.

Analyzing Compatibility of BPEL Processes

The Business Process Execution Language for Web Services provides a powerful technology to aggregate encapsulated functionalities and define high-value Web services - backed by various development and runtime environments of major software companies. Nevertheless, modeling and composing BPEL processes is still a complicated, time and money consuming, and errorprone activity. Formal methods like Petri nets enable the effective analysis of one single BPEL process as well as the comparison of multiple given BPEL models, and the generation of a BPEL model out of another. The current paper presents an prototypically implemented analysis framework that integrates those methods into IBM’s business integration tools. The value of such a framework is illustrated by analyzing behavioral compatibility between BPEL processes, one of the most crucial properties in real-world B2B scenarios.

Consistency between executable and abstract processes

Process models play an all-important role in the development of cross-organizational business processes. On the one hand, the interaction between the participating companies often is specified globally, for example by means of multiple abstract process models - one for each partner. On the other hand, each partner defines its local process autonomously in terms of an executable process model. The important question is whether such an executable model is consistent to the predefined abstract model. This paper describes an approach to prove this property automatically.

Advanced Verification of Distributed WS-BPEL Business Processes Incorporating CSSA-based Data Flow Analysis

The Business Process Execution Language for Web Services WS-BPEL provides an technology to aggregate encapsulated functionalities for defining high-value Web services. For a distributed application in a B2B interaction, the partners simply need to expose their provided functionality as BPEL processes and compose them. Verifying such distributed web service based systems has been a huge topic in the research community lately - cf. [4] for a good overview. However, in most of the work on analyzing properties of interacting Web Services, especially when backed by stateful implementations like WS-BPEL, the data flow present in the implementation is widely neglected, and the analysis focusses on control flow only. This might lead to false-positive analysis results when searching for design weaknesses and errors, e. g. analyzing the controllability [14] of a given BPEL process. In this paper, we present a method to extract dataflow information by constructing a CSSA representation and detecting data dependencies that effect communication behavior. Those discovered dependencies are used to construct a more precise formal model of the given BPEL process and hence to improve the quality of analysis results.

Usability of Web services

This paper is concerned with the application of Web services to distributed, cross-organizational business processes. Web services provide a platform independent concept of components and composition. Thus, they seem to be a proper technology to cover the heterogeneous structures within distributed business processes. Although the technological basis is given, there are a lot of open questions, such as whether Web services fit together in such a way that the composition yields a deadlock-free system - the question of compatibility; whether one Web service can be exchanged by another within a composed system without running into problems - the question of equivalence; and whether we can reason about the quality of one given Web service without considering the environment it is used in. In this paper, we present the notion of usability - our quality criterion of a Web service. This criterion is intuitive and can be easily proven locally. Moreover, this notion allows to answer the other questions.

Advanced verification of distributed WS-BPEL business processes incorporating CSSA-based data flow analysis

The Business Process Execution Language for Web Services WS-BPEL provides an technology to aggregate encapsulated functionalities for defining high-value Web services. For a distributed application in a B2B interaction, the partners simply need to expose their provided functionality as BPEL processes and compose them. Verifying such distributed web service based systems has been a huge topic in the research community lately - cf. [4] for a good overview. However, in most of the work on analyzing properties of interacting Web Services, especially when backed by stateful implementations like WS-BPEL, the data flow present in the implementation is widely neglected, and the analysis focusses on control flow only. This might lead to false-positive analysis results when searching for design weaknesses and errors, e. g. analyzing the controllability [14] of a given BPEL process. In this paper, we present a method to extract dataflow information by constructing a CSSA representation and detecting data dependencies that effect communication behavior. Those discovered dependencies are used to construct a more precise formal model of the given BPEL process and hence to improve the quality of analysis results.

Diagnosing SCA components using WOMBAT

The Service Component Architecture (SCA) is a new technology aiming to simplify application development in a service-oriented architecture. Developing a SCA application basically consists of two major parts: The implementation or discovery of individual components, and the assembly of sets of components. Since each assembly itself might act as a component within a larger application, SCA obviously enables the construction of complex distributed systems that are hardly analyzable. Hence crucial questions like compatibility, consistency or soundness of components need to be answered early during the development process. This paper presents Wombat – an analysis tool that is integrated into IBM’s development environment to perform on demand verification tasks. Wombat benefits from established formal methods for distributed systems. It tailors those methods to relevant use case and puts them into a context that directly supports the development of SCA applications.