Increasingly, distributed systems are being constructed by composing a number of discrete components. This practice, termed composition, is particularly prevalent within the Web service domain. Here, enterprise systems are built from many existing discrete applications, often legacy applications exposed using Web service interfaces. There are a number of architectural configurations or distribution patterns, which express how a composed system is to be deployed. However, the amount of code required to realise these distribution patterns is considerable. In this paper, we propose a novel Model Driven Architecture using UML 2.0, which takes existing Web service interfaces as its input and generates an executable Web service composition, based on a distribution pattern chosen by the software architect.