You will recall from your study of Block l of this course, that a library catalogue constitutes a complete record of the library's collection of documents. Also, you have learnt that the essential functions of a catalogue and the principles upon which it is constructed are not affected by the physical form. Even so, the card catalogue has become by far the most popular form of a library catalogue. In the card catalogue, it is possible for a document to have a number of representations, though practical considerations limit this number. Each document representation (substitute) is in the form of a catalogue card, known as an entry. Each entry indicates some characteristics of the document, such as authorship or subject content. In other words, multiple access points are provided for a document in a catalogue. The entries that indicate the inclusion of documents in classes defined by subject content are known as 'subject entries'. The process of preparing subject entries for documents and organising them for subsequent retrieval is known as Subject Cataloguing.