Katharina Görlach

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.

Conventional Workflow Technology for Scientific Simulation

Workflow technology is established in the business domain for several years. This fact suggests the need for detailed investigations in the qualification of conventional workflow technology for the evolving application domain of e-Science. This chapter discusses the requirements on scientific workflows, the state of the art of scientific workflow management systems as well as the ability of conventional workflow technology to fulfill requirements of scientists and scientific applications. It becomes clear that the features of conventional workflows can be advantageous for scientists but also that thorough enhancements are needed. We therefore propose a conceptual architecture for scientific workflow management systems based on the business workflow technology as well as extensions of existing workflow concepts in order to improve the ability of established workflow technology to be applied in the scientific domain with focus on scientific simulations.

Towards Reference Passing in Web Service and Workflow-Based Applications

In a Service-Oriented Architecture (SOA) based on Web Service technology the services typically communicate with each other by passing data values directly from one service to another. In the case the services are orchestrated by workflows the services receive their input values from the workflow engine and return their calculated results back to the engine by value. In this paper we show several use cases where such value passing behavior has drawbacks. To address this challenge we introduce the concept of pointers in SOA. Pointers allow services to pass their data by reference which is a fundamental advantage for Web Service communication. Furthermore we show an extension of BPEL that introduces reference variables as new type of data containers in workflows. In addition, for the management of pointers we present the Reference Resolution System which can be used in very flexible setups either as central or distributed system.

Dynamic Service Provisioning for the Cloud

This paper introduces a method realizing dynamic provisioning of services in a distributed environment. Depending on a particular state of infrastructure the call of a service can lead to a new instance in the infrastructure or to using an existing instance. Hence, the dynamic deployment allows optimized distribution of service instances within a certain infrastructure. The paper introduces a context model for services that are registered in a distributed runtime environment. Furthermore, algorithms are introduced determining the need for instantiation as well as the best location for deployment. Hence, the best location is determined by correlating the context model, the certain state of infrastructure as well as data transfer costs.

Process space-based scientific workflow enactment

In the scientific field, workflow technology is often employed to conduct computer simulations or computer supported experiments. The underlying IT infrastructure typically comprises resources distributed among different institutes and organisations all over the world. Traditionally, workflows are executed on a single machine while the invoked software is accessed remotely. This approach imposes many drawbacks which are outlined in this paper. To address these weaknesses, we investigate the application of decentralised workflow enactment in the scientific domain. In this context, we explore the employment of process spaces, a middleware for the decentralised execution of workflows. Furthermore, we propose the combination of process spaces with the concept of data references to increase the overall performance of distributed simulations based on workflows. The considerations are discussed with the help of a scenario that calculates and visualises the ink diffusion in water over a period of time.

Towards Simulation Workflows with BPEL: Deriving Missing Features from GriCoL

In this paper, we investigate the suitability of the generalpurpose workflow language BPEL to create executable simulation workflows. We therefore compare BPEL to GriCoL, a graphical language with proven applicability for simulation workflows in Grid environments. We discover a number of incomparable concepts in the two languages. On the one hand, BPEL’s unique features in comparison to GriCoL reveal the rationale behind the approach of using BPEL as basis for a simulation workflow language. On the other hand, based on the features of GriCoL, we are able to discuss how to extend BPEL in order to increase its expressiveness for simulation workflows.

Deployment Aggregates - A Generic Deployment Automation Approach for Applications Operated in the Cloud

One of the most essential requirements to make use of the benefits of Cloud computing is fully automated provisioning and deployment of applications including all related resources. This leads to crucial cost reductions when deploying and operating applications in the Cloud because manual processes are slow, error-prone, and thus costly. Both Cloud providers and the open-source community provide a huge variety of tools, APIs, domain-specific languages, and reusable artifacts to implement deployment automation. However, the meta-models behind these approaches are diverse. This diversity makes it challenging to combine different approaches, avoiding vendor lock-in and tooling lock-in. In this work we propose deployment aggregates as a generic means to use and orchestrate different kinds of deployment approaches. We define a generic meta-model and show its relation to existing meta-models in the domain of deployment automation. Moreover, we discuss how existing artifacts can be used as deployment aggregates as a result of transformation and enrichment.

Views on Scientific Workflows

Workflows are becoming more and more important in e-Science due to the support they provide to scientists in computer simulations, experiments and calculations. Our experiences with workflows in this field and the literature show that scientific workflows consist of a large number of related information. This information is difficult to deal with in a single perspective and has changing importance to scientists in the different workflow lifecycle phases. In this paper we apply viewing techniques known from business process management to (service-based) scientific workflows to address these issues. We describe seven of the most relevant views and point out realization challenges. We argue that the selected views facilitate the handling of workflows to scientists and add further value to scientific workflow systems. An implementation of a subset of the views based on Web services and BPEL shows the feasibility of the approach. The presented work has the goal to increase additionally the acceptance of the workflow technology in e-Science.

A Flexible Engine for the Unified Execution of Service Compositions

This paper presents an engine for the execution of service compositions based on a unified model. The unified model allows to execute service compositions that are specified by use of different languages with different underlying modeling paradigms, e.g. imperative and declarative service compositions by the same engine. Furthermore, the unified model and the presented engines enables the unification of the execution of service orchestrations and the enactment of service choreographies. The flexibility of the presented engine is sophisticated by enabling the instantiation of single engine components and by supporting the distribution of individual service composition instances. The paper discusses the theoretical background of the presented engine and the corresponding unified model in detail. Furthermore, a prototypical implementation as well as an evaluation of the approach is presented.

Unified Execution of Service Compositions (Short Paper)

This paper discusses the unification of service composition based on formal specifications. The approach aims for a unified execution of service compositions that can be modeled by various specification languages covering different modeling paradigms. The unification of service composition models is realized based on formal grammars whereas the unification of service composition execution is realized based on formal queued automata. The approach introduces a classification of context-sensitive grammars for determining an optimized automaton class for the execution of service compositions. Finally, a prototype providing transformations of various modeling languages to formal grammars as well as the grammar-based execution of service compositions is presented.