Various kinds of data are processed in workflow management systems: from case data to control data, from internal data to access to external databases or documents exchanged in inter-organizational workflows. We propose a uniform treatment of all kinds of business data in s. This is achieved by an abstraction mechanism which enables the transparent access to data in any source in a uniform way. We describe an implementation of our extendible generic data access plug-in which provides the workflow management system with updateable XML views of relational data.