BPEL Workflows Combining Standard OGC Web Services and Grid-enabled OGC Web Services

When designing a grid workflow, it might be necessary to integrate different kinds of services. In an ideal scenario all services are grid-enabled. But real workflows often consist of grid-enabled and non grid-enabled services. One reason is that grid-enabling services can be costly. Therefore it is favorable to solely grid-enable the compute-intensive and time-consuming applications. Additionally, workflows should be allowed to include grid jobs that execute legacy applications. Another reason is that very often, third parties charge fees for accessing their services. Hence, it is impossible to convert such a third party service into a service that can be integrated into a grid environment at all. This paper discusses problems of designing a workflow that consists of all these different kinds of services. The geospatial domain is exemplarily used to demonstrate difficulties that workflow designer have to overcome, i.e. constructing a geospatial workflow by using combinations of conventional Web services (XML-based), standard OGC Web services and grid-enabled OGC Web services (WSRF-based). The concept of a workflow engine capable of enacting these workflows is presented and an implementation based on the ActiveBPEL engine is proposed.