Besides the notation in a classification scheme, library material should also include an author indicator, i.e. the first three alphabets of an author's surname. Some libraries may also add a title indicator, date of publication, and/or a copy number. All these elements together, form a Call Number.

The purpose of the call number is to provide the address for an item acquired by the library. This address is where the staff will shelve the item, and where the user can look for the item. The call number also allows a user to browse the collection, to find the available items on any given topic. The idea of creating the call number for each item in the library is that each item can have a unique address. It is the cataloguer's job to determine the specific focus of the item being catalogued, and group the various material dealing with the same topic together. It, thus, creates an organized and accessible collection.

The call number of a document consists of three parts:-