OGSA First Impressions - A Case Study Re-Engineering a Scientific Application with the Open Grid Services Architecture

We present a case study of our experience re-engineering a scientific application using the Open Grid Services Ar-chitecture (OGSA), a new specification for developing Grid applications using web service technologies such as WSDL and SOAP. During the last decade, UCL’s Chemistry de-partment has developed a computational approach for pre-dicting the crystal structures of small molecules. However, each search involves running large iterations of computa-tionally expensive calculations and currently takes a few months to perform. Making use of early implementations of the OGSA specification we have wrapped the Fortran binaries into OGSI-compliant service interfaces to expose the existing scientific application as a set of loosely cou-pled web services. We show how the OGSA implementa-tion facilitates the distribution of such applications across a large network, radically improving performance of the sys-tem through parallel CPU capacity, coordinated resource management and automation of the computational process. We discuss the difficulties that we encountered turning For-tran executables into OGSA services and delivering a ro-bust, scalable system. One unusual aspect of our approach is the way we transfer input and output data for the For-tran codes. Instead of employing a file transfer service we transform the XML encoded data in the SOAP message to native file format, where possible using XSLT stylesheets. We also discuss a computational workflow service that en-ables users to distribute and manage parts of the computa-tional process across different clusters and administrative domains. We examine how our experience re-engineering the polymorph prediction application led to this approach and to what extent our efforts have succeeded