Abstract | | A programmable overlay network goes beyond existing Grid applications, as it enables nodes to actively participate in a distributed computation as opposed to simply share their information and computational resources. In this talk we will discuss the challenges involved in programming such overlay network. These are not limited to the decentralized and distributed nature of the overlay but also involve the difficulty of orchestrating the data and computational services provided by different and heterogeneous nodes. To this end, we claim that workflow languages can provide appropriate high level abstractions for specifying the flow linking the services provided by the nodes of the overlay. In particular, we will present JOpera, an advanced workflow tool for modeling and efficiently executing large scale distributed computations that is being extended to overlay networks in the context of the AEOLUS EU project. JOpera provides an integrated environment built on the Eclipse platform to support the whole life cycle of such overlay programs: development, execution, monitoring and debugging. A short demo will be given, showing the main features of JOpera's visual composition language and emphasizing the extensibility of JOpera's plugin-based architecture. Among many others, JOpera's growing user community includes the Swiss National Supercomputing Center, the Swiss Bioinformatics Institute, NCSA and the Rosen Center for Advanced Computing (at Purdue University). JOpera can be freely downloaded from www.jopera.org. |