Integration of clinical research data and routine care data, in order to streamline the process of conducting clinical studies, has been a problem for quite a while now. The Single Source project at the University of Münster aims at contributing to this area. The approach is based on a vast usage of XML technology together with a novel integration architecture. The emphasis in this paper is on the former: The seamless usage of XML technology throughout the entire application is presented, and mismatches of programming paradigms are averted by exploiting the features of XML, XQuery and XForms. In particular, this is demonstrated by the example of a component used for handling forms, by how it is built and used in the entire scenario.