Section: Application Domains

Web services and active structured documents

Keywords: Active documents, Web services, choreographies, orchestrations, QoS.

Web services architectures are usually composed of distant services, assembled in a composite framework. This raises several practical issues: one of them is how to choose services, assemble them, and coordinate their executions in a composite framework. Another issue is to guarantee good properties of a composite framework (safety but also QoS properties). All this has to be done in a context where a distant service provided by a subcontractor is only perceived as an interface, specifiying legal inputs and outputs, and possibly a quality contract.

The standard in industry for Web-services is now BPEL  [57] , but most of the problems listed above are untractable for this language. Composition of services can also be performed using choreography languages such as ORC  [69] . The implementation of orchestration and choreography description languages raises a number of difficulties related to efficiency, clean semantics, and reproducibility of executions, issues of composite QoS associated with orchestrations. We develop studies in these areas, with the aim of proposing service composition frameworks equiped with tools to specify, but also to monitor and analyse the specified architectures.

Another issue is the convergence between data and workflows. Web Services architectures are frequently considered exclusively as workflows, or as information systems. Many approaches to Web Service orchestration and choreography abstract data away. Symmetrically, modern approaches to Web data management typically based on XML and Xqueries rely on too simplistic forms of control. We develop a line of research on Active documents. Active documents are structured data embedding references to services, which allow for the definitions of complex workflows involving data aspects. The original model was proposed by S. Abiteboul  [56] , but the concept of active document goes beyond AXML, and offers a document oriented alternative to Web services orchestrations and choreographies. This approach is in particular well adapted to the modeling of E-business processes, or information processing in organizations, etc. Our aim is to extend and promote the concept of active document. This means developing verification and composition tools for document-based architectures, considerd not only as theoretical models but also as effectively running systems. To this extend, we develop an active document plateform.