Factors Governing Subject Indexing Systems 

There are many factors that govern the design of subject heading systems. Some of the more important ones are: 

1. content analysis of documents to select the right key words that represent their specific subject; 
2. rendering the selected key words in a logical sequence according to prescribed principles and postulates; 
3. establishing main and added entries in standard formats; 
4. provision of  cross references to  subject concepts to obtain as  many relevant documents as are available in the library through catalogue or index file; and 
5. arrangement of entries. 

Content analysis of documents is totally  independent of any technique of indexing. Skills required in this process  are the subject background of the indexer on the subject(s) indexed and the ability to read/scan documents fairly quickly for the purpose of identifying appropriate key words to represent the thought contents of documents. 

To know what a document is about, some of the aids available in the documents themselves are: Titles  and sub-titles, if any; content page(s) with all the details of chapters listed; foreword, preface; conspectus; introduction;  the text - a quick scanning of the body of the text; and the index. Sometimes the  captions in tables, diagrams,  etc. and book jacket serve as an useful  aid. In addition to all these aids, dictionaries, encyclopaedias; handbooks, guides etc. are useful  consulting aids to know the subject(s). It may also be necessary on occasions to consult subject experts to know subject ramifications and their importance. 

For the rest  of the factors mentioned above, indexing systems usually provide the necessary guidelines, rules and procedures, backed up by principles, postulates, etc. which would explain the designer's logic and philosophy of approach. The understanding of all these and their proper assimilation by indexers would ensure a fairly good quality subject index.