XML is becoming the universal format for data exchange between applications. Recently, the emergence of Web services as standard means of publishing and accessing data on the Web introduced a new class of XML documents, which we call intensional documents. These are XML documents where some of the data is given explicitly while other parts are defined only intensionally by means of embedded calls to Web services.When such documents are exchanged between applications, one has the choice to materialize the intensional data (i.e. to invoke the embedded calls) or not, before the document is sent. This choice may be influenced by various parameters, such as performance and security considerations. This paper addresses the problem of guiding this materialization process.We argue that, just like for regular XML data, schemas (ala DTD and XML Schema) may be used to control the exchange of intensional data and, in particular, to determine which data should be materialized before sending a document, and which should not. We formalize the problem and provide algorithms to solve it. We also present an implementation that complies with real life standards for XML data, schemas, and Web services, and is used in the Active XML system [3,1]. * This project is partially supported by EU IST project DBGlobe

Abstract. This paper deals with some modeling aspects that have to be addressed in the context of the integration of heterogeneous and autonomous XML resources. We propose an integration system, but the emphasis of this paper is neither on its algorithmic aspects nor on its technical details. Instead, we focus on the significance of offering appropriate high-level primitives and mechanisms for representing the semantics of XML data. We posit that support for such primitives and mechanisms is a pre-requisite for realizing the goals of the semantic Web.

In this paper we propose a mediator architecture for the querying and integration of Web-accessible XML data sources. Our contributions are (i) the definition of a simple but expressive mapping language, following the local as view approach and describing XML resources as local views of some global schema, and (ii) efficient algorithms for rewriting user queries according to existing source descriptions. The approach has been validated by the ¦ § © prototype. © or a variable, as in rule © ¢. The XPath pattern is called the location path of the rule. The LHS of a rule also contains a variable declaration (the use of variables will be explained later). The RHS of a mapping rule is a path in the global schema, called the schema path of the rule. Mapping rules define instances of concepts and relationships between them. As an example for the first case, consider the rule © in Fig. 4. It states that the elements of type Painter, children of the root elements of the XML documents in are (descriptions of) instances of concept Person. As an example for the second case, rule © ¢ specifies that the value obtained by evaluating XPath pattern @name on some XML element returned by rule © , corresponds to a value of attribute has name of (is an instance of concept Person). In the same way, rule © ¢ ¡ connects all instances obtained by rule © to all instances of concept Man Made Object obtained by following the path carried out.produced. This view of mapping rules allows us to define the semantics of XML fragments and their structural relationships in terms of the global derived schema. Thus, © defines a subset of the extent of concept Person, while rule © ¢ ¡ relates elements in this subset by the derived role carried out.produced to a subset of the extent of Man Made Object. 2.4 Query Processing Users formulate queries on the global schema using a simplified variant of OQL, the standard for querying object databases.