Components of an IRS 

Lancaster [1979] considers that an Information Retrieval System (IRS) comprises the following components: 

i)  the document selection sub-system 

ii)  the indexing sub-system 

iii)  the vocabulary sub-system 

iv)  the searching sub-system 

v)  the sub-system of interaction between the user and the system (i.e., user interface) 

vi)  the matching sub-system, that is, the system that matches the document representations against the user requirements. 

All the above mentioned sub-systems are utilised in the performance of the following activities: 

1. information resource building, 
2. database creation and maintenance, and 
3. Information retrieval and dissemination.