Guarded Active XML (GAXML) was proposed by Abiteboul, Segoufin, and Vianu, as a high-level specification language tailored for data-intensive, distributed, dynamic Web services. GAXML consists in XML documents with embedded guarded service calls, thus allowing for the definition of control flows in documents. In this paper we enhance GAXML with the concepts needed to satisfy the requirements of ``Service Computing'' and ``Service Oriented Architectures''. We provide a richer model for external services in the form of interfaces. Specifying an interface consists in describing, using patterns: 1/ the shape of documents that can serve as parameters to a call, and 2/ the possible returns of a call. Our notion of interface comes with a notion of implementation --- a service implements an interface --- that builds upon the known concept of containment and a new concept of satisfaction. Then, we propose Distributed Active AXML (DAXML) as a model of guarded active XML systems distributed over a set of peers. Peers transform distributed documents in response to service calls from their own or other peers in an asynchronous way. DAXML schemas compose, thus capturing the mechanism of replacing an external service call by a distant call to an implementation of it, offered by another peer. DAXMLschemas and documents can be refined by replacing, in documents, external service calls by respective implementations thereof; the symmetric operation is service abstraction. Abstracting services as interfaces is an efficient tool in simplifying analyses of DAXML documents. We illustrate our approach on a representative example combining data and workflow management, namely the Dell supply chain.