ABSTRACT
The subject analysis of reports is a most important operation since it perhaps demands more skilled effort than any other task in an information centre, and the success or failure of later information retrieval operations depends on how well the original subject analysis was done. Information retrieval with pre-co-ordinated manual systems is the simple visual operation of scanning cards in a card catalogue or subject heading entries in a bookform index. Indexing systems may be divided into pre-co-ordinate and post-co-ordinate systems according as to whether the co-ordination of the indexing terms to form the concepts required for retrieval takes place at the indexing stage or at the retrieval stage. The basis of post-co-ordinate indexing usually is the list of subject indexing terms called a 'thesaurus'. An early form of computer-produced index which has proved to be of lasting value is the Key Word in Context introduced by H. P. Luhn and used by the American Chemical Society in Chemical Titles.
