The system is composed of three layers of software as illustrated in Figure 1. 

In addition, an ASP infrastructure (hardware & software) should provide the necessary machinery to run the system. We now introduce the layers in a bottom up approach

Figure 1

• The Web Site Design and Development toolkit supports the WebML model and incorporates visual (graphical) interfaces for defining the data structure and hypertext behavior of Web applications.
• The Active Documents Editor will support the definition of types of active documents consisting of an XML Schema and an associated flow, specified in ADFL, the Active Document Flow Language

The Service Composition Layer will operationally support the composition and orchestration of Web Services either developed in the project through the Data Integration suite or the upper layers, or available on the Intranet/Internet.

• The WebML code generator will be extended with translation functions for mapping the high-level service composition primitives added to the WebML language into runtime components capable of managing complex conversations with Web services.
• The Active Document Engine, i.e. the interpreter of active documents, will be developed as a Web service itself, so to be interoperable with any WebML-specified and generated application. The engine will process an active document by running the composition of services described by its associated flow. The results will be collected in place within the document.

The Data Integration Layer is composed of the Data Integration suite of components, which transforms a set of local or remote data sources in an XML view accessible as a Web service through XQuery, the W3C XML query language.

• The XML Mediator integrates heterogeneous data sources through local wrappers and processes distributed queries by delegating sub-queries to the sources.
• The XML Repository manages persistent collections of XML documents in a native XML file system and provides query access to them.