opac An Online Public Access Catalog (often abbreviated as OPAC or simply Library Catalog) is an online database of materials held by a library or group of libraries. Users search a library catalog principally to locate books and other material physically located at a library. (Excerpt from Wikipedia article: OPAC) 97 195 5.7 5.6 11 61.6 http://www.ariadne.ac.uk/sites/all/datacharts/hc/1183-chart-wp.html copac Copac is a union catalogue which provides free access to the merged online catalogues of many major university research libraries in the United Kingdom and Ireland, plus an increasing number of specialist libraries and the British Library, the National Library of Scotland and the National Library of Wales. It has over 35 million records from over 50 libraries, representing a wide range of materials across all subject areas. Copac is freely available to all. (Excerpt from Wikipedia article: Copac) 38 152 2.2 http://www.ariadne.ac.uk/sites/all/datacharts/hc/1647-chart-wp.html