Background to the thesaurus

Origins

The African Studies Thesaurus is the culmination of a two-pronged project designed to transform the ASC Leiden library catalogue into a comprehensive bibliographical tool in the field of African Studies and facilitate total and easy national and international access to Africa resources. The project was initiated in 1998 and in 1999 received funding from NWO, the Netherlands Organization for Scientific Research.

The first prong, the conversion of the library’s card catalogue into electronic form, involved the retrospective online cataloguing of some 75,000 titles and was completed in 2000.

The second prong, started in 1999, aimed to convert the numerical codes used for subject access in the library’s online catalogue into a more user-friendly word-based system. The codes, based on the UDC (Universal Decimal Classification), had been derived from successive editions over a period of almost 50 years, and had, generally, not been updated. Moreover, the codes had also been adapted to suit the specific requirements of an African Studies collection. An analysis of the structure and consistency of these codes and an assessment of existing language-based subject indexing systems used in other Africana libraries led to the conclusion that there was no ready-made word-based system which suited our needs. We therefore decided to build our own African Studies Thesaurus.

Thesaurus construction

After an initial phase in which the technical and organizational aspects of the project were charted and a thesaurus building tool was selected, work on “translating” the UDC codes into descriptors and building a thesaurus began in 2001. In the course of the following years modules for African Languages (350 preferred terms), African Peoples (1200 preferred terms) and African Polities (300 preferred terms) were developed for experimental use and placed on the ASC website. By March 2006 the last UDC codes had been “thesaur-ised”. More than 8,500 UDC codes had been “translated” into some 5,200 descriptors (preferred terms) and embedded in a thesaurus structure, with cross-references (c. 6,900 non-preferred terms), hierarchical and associative relationships .

The challenge of the project has been to combine two analytically distinct activities inextricably linked in practice – the construction of a thesaurus on the one hand, and the conversion of (UDC) codes into descriptors on the other. The conceptual differences between a numerical code in a classification and words in a natural language were brought home with force. The task was further complicated by inconsistent classification practice over the years and shifts in the meaning and coverage of codes. There was often no one-to-one match between a code and a thesaurus descriptor and a good many previously assigned UDC codes had to be “cleaned up”. Because of the many different kinds of relations between codes and descriptors, the automatic conversion of all the UDC codes assigned to titles in the ASC catalogue into descriptors was a technically complex process.

Implementation

An ongoing concern throughout the project was the implementation and operationalization of the thesaurus in cooperation with OCLC PICA, which hosts the library’s online catalogue. For a number of reasons it was decided not to integrate the thesaurus fully into the catalogue but to make it available on the ASC website instead, with reciprocal links between the catalogue and the thesaurus. In April 2006 the first steps to operationalize the thesaurus were taken. This was followed by the conversion of all the UDC codes into descriptors and the incorporation of descriptors in the catalogue. With the publication of the African Studies Thesaurus on the ASC website in June 2006 the project was completed.