Peer-to-peer systems are gaining increasing popularity as a scalable means to share data among a large number of autonomous nodes. Since the shared data are unstructured and they do not follow a global schema, XML-based descriptions of the data can be used to provide a uniform way to query the heterogeneous data. In our research, we are interested in designing a fully decentralized approach for the problem of espciently routing path queries among the nodes of a peer-to-peer system. Our approach is based on (a) selecting and maintaining specialized data structures, called filters that efficiently summarize the content, i.e., the documents, of one or more node and (b) using these filters to build an overlay network that groups together nodes with similar content.