SUBJECT INDEXING SYSTEMS 

You have learnt that one of the most important functions of a  library catalogue is to provide access to documents in a library through their subject contents. A classified catalogue facilitates subject approach to documents in a library by subject arrangement of document surrogates in an organised and systematic way by using a system of classification chosen for the library. Nevertheless, an alphabetical subject index to the classified part of the catalogue is essential as the notation of the classification system (class numbers), by which the main entries of documents are arranged, is not obvious to most readers. A dictionary catalogue, however, provides this facility of  subject approach through verbal subject representation of the content of documents. It should, therefore, be clear that irrespective of the inner forms of library catalogues, verbal subject headings are essential to satisfy subject approach to documents in a library. Just as we have codes for descriptive cataloguing that provide rules and procedures with reference to the choice and rendering of bibliographical data of documents, indexing systems have been designed and developed with their own standard rules and procedures for constructing subject headings.