DXL: Data eXchange Language

With large volumes of data being exchanged over the Internet query languages are needed to bridge the gap between databases and the web. DXL provides an extendible framework, designed to exchange data between heterogeneous sources and targets, such as databases and XML documents. One application of DXL, the focus in this article, is to retrieve data from databases and yield the result in XML documents. The major contribution of DXL compared to other query languages, like RXL and XQuery, is that the structure of an output XML document may depend not only on the DXL query but also on the source data. To achieve this DXL uses a construct clause, where the structure of the XML document is (partially) defined, but unlike other XML query languages this clause is embedded in a template, which can be called recursively. We demonstrate the power of DXL with a newsgroup example, where each posted message may have arbitrarily nested follow-ups. The extendibility of the framework is ensured by using XML to describe the syntax of DXL. Besides discussing the syntax, semantics, and the newsgroup application of DXL, we will also show how heterogeneous sources can be queried and integrated into a single XML document, and we discuss the architecture that is setup to implement DXL.