Aiming at quality and coverage combined: blending physical and virtual union catalogues

This article discusses the deficiencies of search engines and the importance of metadata before examining three models of metadata retrieval: distributed; distributed data with a centralised index; and centralised union catalogue. In listing the advantages and disadvantages of the distributed model, the Z39.50 protocol is used as an example. The OAI harvest protocol is the example of the second model. Virtual union catalogues are compared with a real one. A pan‐European model is discussed as a way to combine the best of all three models, with EUCAT as its base.