Next generation Digital Libraries (DLs) will offer an entire ensemble of systems and services designed to help users to easily find and access the information they are looking for. However, much work is still required in order to achieve this vision. In this paper, we concentrate our attention on devising techniques allowing an effective routing of queries, which we think can be of the utmost importance in providing effective and efficient querying in heterogeneous and distributed DLs, identifying the best ways to navigate the available nodes and, thus, the documents (or their parts) which are most suitable to best answer the user needs. We describe a routing mechanism, which we call routing by mapping, in which the query is sent to the DL ...