A library catalogue (or library catalog) is a register of all bibliographic items found in a library or group of libraries (such as a network of libraries at several locations). A bibliographic item can be any information entity (e.g., books, computer files, graphics, realia, cartographic materials, etc.) that is considered library material (e.g., a single novel in an anthology), or a group of library materials (e.g., a trilogy), or linked from the catalog (e.g., a webpage) as far as it is relevant to the catalog and to the users (patrons) of the library.
Charles Ammi Cutter made the first explicit statement regarding the objectives of a bibliographic system in his Rules for a Printed Dictionary Catalog in 1876. According to Cutter, those objectives were
1. to enable a person to find a book of which either (Identifying objective)
2. to show what the library has (Collocating objective)
by a given author
on a given subject
in a given kind of literature
3. to assist in the choice of a book (Evaluating objective)
as to its edition (bibliographically)
as to its character (literary or topical)
Traditionally, there are the following types of catalogue:
Author card: a formal catalog, sorted alphabetically according to the authors' or editors' names of the entries.
Title catalog: a formal catalog, sorted alphabetically according to the title of the entries.
Dictionary catalog: a catalog in which all entries (author, title, subject, series) are interfiled in a single alphabetical order. This was the primary form of card catalog in North American libraries just prior to the introduction of the computer-based catalog.
Keyword catalog: a subject catalog, sorted alphabetically according to some system of keywords.
Mixed alphabetic catalog forms: sometimes, one finds a mixed author / title, or an author / title / keyword catalog.
Systematic catalog: a subject catalog, sorted according to some systematic subdivision of subjects. Also called a Classified catalog.
Shelf list catalog: a formal catalog with entries sorted in the same order as bibliographic items are shelved. This catalog may also serve as the primary inventory for the library.
Cataloging (or cataloguing) rules have been defined to allow for consistent cataloging of various library materials across several persons of a cataloging team and across time. Users can use them to clarify how to find an entry and how to interpret the data in an entry. Cataloging rules prescribe -> which information from a bibliographic item is included in the entry; -> how this information is presented on a catalog card or in a cataloging record; -> how the entries should be sorted in the catalog. The larger a collection, the more elaborate cataloging rules are needed. Users cannot and do not want to examine hundreds of catalog entries or even dozens of library items to find the one item they need.