In service-oriented Grid computing, great emphasis is placed on platform independence and cross-platform interoperability at the price of a higher initial software development complexity and cost. The Model Driven Architecture (MDA) approach to software development promises to reduce costs and increase reliability and flexibility of such complex distributed systems. In this paper, we introduce an MDA approach to service-oriented Grid application development and its prototypical implementation. To enable a better separation of development concerns, we propose a subdivision of the Platform Specific Model (PSM) into two parts, separating application functionality and Grid logic. This separation of concerns is maintained even at the code level using Java annotations, allowing domain experts to work on every level with only limited knowledge outside of their domain.