The broadly defined mission of the Biomedical Informatics Research Network (BIRN, www.nbirn.net) is to better understand the causes human disease and the specific ways in which animal models inform that understanding. To construct the community-wide infrastructure for gathering, organizing and managing this knowledge, BIRN is developing a federated architecture for linking multiple databases across sites contributing data and knowledge. Navigating across these distributed data sources requires a shared semantic scheme and supporting software framework to actively link the disparate repositories. At the core of this knowledge organization is BIRNLex, a formally-represented ontology facilitating data exchange. Source curators enable database interoperability by mapping their schema and data to BIRNLex semantic classes thereby providing a means to cast BIRNLex-based queries against specific data sources in the federation. We will illustrate use of the source registration, term mapping, and query tools.