Dynamic Workflows for Grid Applications

In the Grid computing community, there are several approaches to execute not only single tasks on single Grid resources but also to support workflow schemes that enable the composition and execution of complex Grid applications. The most commonly used workflow model for this purpose is the Directed Acyclic Graph (DAG). Within the establishment of the Fraunhofer Resource Grid, we developed a Grid Job Definition Language (GJobDL) that is based on the concept of Petri nets instead of DAGs to support the graph-based definition of arbitrary workflows on an abstract level. During the workflow execution, the abstract workflow must be concretized in order to be mapped onto the real Grid environment. This requires dynamic completion of the workflow based on actual information. It may be necessary to introduce new tasks – such as data transfers, deployment of software, authorization request, and data retrievals. These tasks can be represented by sub Petri nets that replace parts of the existent Petri net during runtime of the Grid application. We also propose a concept for fault management of entire job workflows by explicitly modeling the fault management within the workflow model. This fault management can be user-defined or be realized automatically by introducing new tasks enabling fault management based on fault management templates.