From classification to thesaurus... and back? Subject indexing tools at the library of the Afrika-Studiecentrum Leiden

The paper describes an approach to thesaurus creation and use. An African Studies Thesaurus was constructed for the purpose of subject indexing and retrieval in the Library of the African Studies Centre (ASC) in Leiden in 2001-2006. A word-based system was considered a more user-friendly alternative to the UDC codes which were used for subject access in the ASC catalogue at the time. In the process of thesaurus construction UDC codes were used as a starting point. In addition, when constructing the thesaurus, each descriptor was also assigned a UDC code from the recent edition of the UDC Master Reference File, thus replacing many of the old UDC codes used by then, some of which dated from the 1952 French edition. The presence of the UDC codes in the thesaurus leaves open the possibility of linking the thesaurus to different language versions of the UDC MRF in the future. Over a period of five years some 8,500 UDC codes from all classes of the UDC, a majority from class 3, and to a lesser extent classes 6, 8 and 9, were "translated" into thesaurus descriptors and structured according to basic thesaurus relationships (BT, NT, RT, UF/USE). In a parallel but separate operation each UDC code which had been assigned to an item in the library's catalogue was subsequently converted into one or more thesaurus descriptors.