A pre-relational databases datamodel. "Preceeded" by the relational model since the flexibility of this makes it hard to work with. Now re-invented in RDF :)
T. Joachims, L. Granka, B. Pan, H. Hembrooke, and G. Gay. SIGIR '05: Proceedings of the 28th annual international ACM SIGIR conference on Research and development in information retrieval, page 154--161. New York, NY, USA, ACM, (2005)