XML is becoming a standard to represent and exchange structured data over the Web. Undoubtedly, more and more data on the Web will be in XML form, as more and more DTDs will be available to describe it. Given this, the Xyleme project proposes to study and build a dynamic World Wide XML distributed data warehouse, capable of storing a very large number of XML data available on the Web. Among the many problems addressed by the Xyleme project, in this paper, we focus on query processing in Xyleme. In particular: (i) how to query an integrated view, (ii) how documents are indexed in the repository, and (iii) how the algebraic plans are distributed and evaluated.