Role of a Thesaurus in Indexing and Searching 

The thesaurus contributes to consistency in  indexing between indexers and reduces incorrect term assignments to a great extent because of the provision of the term definition or scope note. This is particularly true if descriptors, which are some what related, are carefully distinguished by scope notes.  

Thesaurus plays the following two roles 

a)  prescriptive role. It prescribes as to  what term  should be assigned. The 'use' reference is a prescriptive indicator. 

b)  suggestive role. It suggests terms to be  considered instead of, or in addition to etc. The RT (and to a certain extent the BT and NT) are suggestive indicators.