Post-Coordinate Indexing Systems 

These systems arc also called coordinate indexing systems. As in the pre-coordinate systems, the starting point, here too, is the identification of multi-concept subjects and their compound concepts from the documents to be indexed. Once the multi-concept subject is analysed into its elementary  compound concepts, entries are prepared under terms, which represent elementary concepts. In other words, by this method only simple subject concepts are indexed. These concepts are not coordinated at the time of preparation of catalogue or index. Since the coordination of concepts does not take place till such time a request is made by user for information about a particular compound subject, this method of indexing is called post-coordinate or sometimes simply, coordinate indexing. In its early stages, post-coordinate indexing employed subject concepts as they were expressed in the document for index description of the document. Although, indexing can thus be done in 'natural language' (i.e., by using significant words taken directly from. the document) but in many  cases, post-coordinate indexing language employees terms which mostly represent isolate concepts and are not in the form of compound subject headings. For example, if we have a document dealing with the compound subject "Computer Cataloguing in Libraries", the subject analysis of the document may consist of three simple concepts namely,  

COMPUTERS 

CATALOGUING 

LIBRARIES 

The document is indexed under each of these simple concepts and index entries are prepared. Thus, the compound subject of the document receives an index description consisting of their concepts entered individually in the index. If a user is interested only in documents dealing with the compound subject then he has to coordinate all these terms at the search stage and retrieve the documents dealing with the compound subject. This is  accomplished by retrieving documents containing common document numbers under individual component concepts. Let us, consider another document representing the subject 'Torsion in the Reinforced Concrete in Service Cores in Tall Buildings'. This multi-concept subject may be analysed into the following unit or elementary concepts: 

Torsion 

Reinforced

Concrete 

Service

Cores 

Tall Buildings 

If it is intended to  prepare post-coordinate index for this example, we may  have to prepare entries under the following index headings: 

Buildings, Tall 

Concrete,

Reinforced 

Service Cores 

Torsion