Alphabetical index:

The alphabetical index to a classified catalogue; consisting of author, title (wherever necessary), subject entries and other entries for collaborators, series, editors of series, and a host of cross references, is meant to support the classified part of the catalogue. It can fulfil all the functions of a dictionary catalogue i.e., collect the works of an author together, bring all the different editions of a title, cross references for subjects, etc. With the classified part bringing all the related subjects together, and the alphabetical order bringing together all the distributed relatives, the classified catalogue can fulfil all the functions of a library catalogue. 

Despite all these features of a classified catalogue, it has its own merits and limitations. Both these aspects are discussed below:  

Merits 

a)  The greatest merit of a classified catalogue is that it provides a logical subject-wise guide to the materials available in a library. In other words, it brings together in one place all the entries relevant to a particular subject with all its related subjects. 

b)  The arrangement of entries in the catalogue reflects the arrangements of documents on the shelves of the library. 

c)  The reader is not shunted from one end of the catalogue to the other for finding the materials of his interest from the catalogues. 

d)  Subjects without inconvenience can bring our the printed versions of the catalogue in parts. 

e)  At one glance, it reveals the strength and weakness of different subjects represented by the library collection. 

It facilitates compilation of reading lists and subjects bibliographies for special purposes. Changes in the terminology of the subjects do not affect the arrangement of entries in the classified part of the catalogue.