As the Web comes to be viewed as a large semistructured database with XML as its model, issues relatedto querying semistructured data in general, and XML in particular, become more important. In thispaper, based onthe MIX and W4F,a system of integrating and accessing heterogeneous data sources is presented. The system accessesa set of XML sources, which are currently information systems wrapped to provide (1) an XML view of their dataand (2) a set of XMAS queries that they can answer. Conceptually, it exports an integrated view of the source data.The view definition, provided by the view developer, specifies how the source data will be integrated. Especially, thewrapper for Web data sources is generated by the W4F and the system does not materialize the integrated view in ad-vance.
