Session C1 1. Employing WS-BPEL Design Patterns for Grid Service Orchestration using a Standard WS-BPEL Engine and a Grid Middleware

In BIS-Grid, a BMBF-funded project in the context of the German D-Grid initiative (http://www.d-grid.de), we focus on employing Grid technologies for information systems integration. The goal is to enable small and medium enterprises (SMEs) to integrate heterogeneous business information systems and to use external Grid resources and services with reasonable effort. To achieve this goal, we develop a Grid workflow middleware – the BIS-Grid engine – that is capable to orchestrate WSRF-based Grid Services. This engine is based upon service extensions to the UNICORE 6 Grid middleware, using an arbitrary WS-BPEL workflow engine. WS-BPEL is an XML format for workflow description and the industry de-facto standard language for service orchestration. One main design decision in BIS-Grid is to leave the WS-BPEL language unmodified to avoid incompatibility with commercial WS-BPEL engines, nor to modify a WS-BPEL engine to ensure its exchangeability and hereby the sustainability of the BIS-Grid engine [1]. Thus, our UNICORE 6 service extensions fill the gap between WS-BPEL and the Grid world. This is in contrast to other approaches where WS-BPEL for Grid Service orchestration is utilised. For example, in [2] a solution is presented that is based on extending BPEL4WS, the predecessor of the WS-BPEL language, also requiring extensions to the workflow engine. This leads to a proprietary solution in which the workflow engine is not exchangeable. Our design decisions led to several technical challenges. Some are solved by applying so-called WSBPEL design patterns. One category of patterns is called Grid utilisation patterns, which describe how to invoke stateful WSRF-based Grid Services with standard WS-BPEL. The development of these patterns is partly based on work by Ezenwoye et al. [3]. Since we regard the application of Grid utilisation patterns as workflow designer tasks, we plan to provide a workflow design tool that supports their application. Another identified design pattern category is called implementation-specific patterns. Patterns of this category address architecture specific details that arise within BIS-Grid [1]. For each active workflow, there exist two instances, a workflow service instance in the UNICORE 6 service container, and a workflow instance in the WS-BPEL engine. Implementation-specific patterns describe how these instances are mapped to each other. Since implementation-specific patterns do not represent functional logic of the workflow, they have to be concealed from workflow designers. Thus, they are inserted automatically within the UNICORE 6 extensions. This paper presents and discusses the identified WS-BPEL design patterns for Grid Service orchestration. Thereby, we focus on Grid utilisation patterns and implementation-specific patterns. The approach is illustrated by the example of the BIS-Grid engine, which is developed by the BIS-Grid project, using ActiveBPEL as WS-BPEL workflow engine and UNICORE 6 as Grid Service container. However, our patterns are intended to address WS-BPEL-based Grid Service orchestration in general. This means that any WSRF-compliant middleware such as Globus Toolkit 4 can be used as Grid Service container. Accordingly, we emphasise the technical issues, present the general solution approach and provide examples on pattern application. Beforehand, we discuss similar approaches and related work. We also describe the implementation of automatic Grid pattern injection and conclude the paper with an overview on our future work in this area.