"When the IDRC Library began to index the material in its collection and to build a data base using the ISIS computer systems, the OECD's Macrothesaurus was selected as the source of descriptors for indexing and retrieval. At that time it was hoped that the international and other organizations also using the Macrothesaurus would construct a joint operation to keep it up to date and to modify it in the light of experience. These hopes have not so far been realized, and, while there have been considerable ad hoc consultations among some of the major users of the Macrothesaurus, each has had to make modifications unilaterally to meet individual requirements. IDRC's policy has been to stay as close as possible to the Macrothesaurus, and to make changes only when necessary. Nevertheless, hundreds of changes in matters of detail have had to be introduced over the years since operations began; the original structure of the Macrothesaurus has, however, been retained."