Functions of an IRS 

Information Retrieval (IR) is best understood if one remembers the information being processed consists mainly of documents. In that context, IR deals with representation, storage and access to documents or information surrogates. In other words, the input information is likely to include natural language text or document excerpts and abstracts. The output of an IRS in response to a search request consists of sets of references. These references are intended to provide the system users the information about the items of interest to them.    

Usually, an IR system is considered to have the function of "leading the user to those documents that will best enable him/her to satisfy his/her need for information" [Lancaster, 1979 Lancaster indicates the major functions of an Information Retrieval System through the enclosed diagram.  

It may be mentioned here that the information to be stored is often available in the form of natural language texts, and the mechanisms used to represent the texts include both controlled and uncontrolled vocabularies which separately or in combination constitute the 'indexing language. The indexing process transforms the natural language text of the information into elements of the indexing language, and. the search formulation process converts statements of information need into elements of the same indexing language. The identification of information items to be retrieved then depends on the item representations rather than the original natural language texts of the items. The organisation of the items in the file has a great deal to do with efficiency of search and retrieval.