Preserved Context Index System (PRECIS) 

PRECIS (Preserved Context Index System) was designed and developed by Derek Austin by about 1970 as an alternative procedure for deriving the subject headings and subject index entries for British National Bibliography  (BNB). Since 1952, for nearly 20 years, BNB followed chain procedure for deriving subject index entries. Two most  important factors worked for the development of PRECIS: I) Idea of replacing chain indexing technique of BNB; and ii) the decision of  the British Library to generate computer produced BNB  with all the indexes in  view of launching the UKMARC project. Accordingly, a research project for a suitable alternative for generating subject indexes directly from the machine readable records were undertaken by the British Library with the following objectives, which, ultimately resulted in the development of PRECIS: 

1. The computer, not the indexer, should produce all index entries. The indexer's responsibility would be only to prepare the input strings and to give necessary instructions to the computer to generate indexes according to a definite format; 
2. Each of the sought terms should find index entries and each entry should express the complete thought content/full context of the document  unlike the chain indexing where only one entry is fully co-extensive with the subject and others are cross references describing only  one  aspect of the complete  content of the document; 
3. Each of the entries should be expressive; 
4. The system should be based on a single set of logical rules to make it consistent; and 
5. The system must have sufficient references for semantically related terms. PRECIS is now a recognised indexing model and has been adopted by a number of indexing agencies to produce subject indexes to a wide range of indexing tools like national bibliographies, library catalogues, indexes to audio-visual materials,  musical scores, micro documents, etc.