A library catalog (or library catalogue) 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.
The card catalog was a familiar sight to library users for generations, but it has been effectively replaced by the online public access catalog (OPAC). Some still refer to the online catalog as a "card catalog". Some libraries with OPAC access still have card catalogs on site, but these are now strictly a secondary resource and are seldom updated. Many of the libraries that have retained their physical card catalog post a sign advising the last year that the card catalog was updated. Some libraries have eliminated their card catalog in favour of the OPAC for the purpose of saving space for other use, such as additional shelving.
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)
3. to assist in the choice of a book (Evaluating objective)
These objectives can still be recognized in more modern definitions formulated throughout the 20th century. 1960/61 Cutter's objectives were revised by Lubetzky and Lubetzky and the Conference on Cataloging Principles (CCP) in Paris. The latest attempt to describe a library catalog's goals and functions was made in 1998 with Functional Requirements for Bibliographic Records (FRBR) which defines four user tasks: find, identify, select, and obtain.
Traditionally, there are the following types of catalog:
Library catalogs originated as manuscript lists, arranged by format (folio, quarto, etc.) or in a rough alphabetical arrangement by author. Printed catalogs, sometimes called dictionary catalogs enabled scholars outside a library to gain an idea of its contents. These would sometimes be interleaved with blank leaves on which additions could be recorded, or bound as guardbooks in which slips of paper were bound in for new entries. Slips could also be kept loose in cardboard or tin boxes, stored on shelves. The first card catalogs appeared in the nineteenth century, enabling much more flexibility, and towards the end of the twentieth century the OPAC was developed (see below).
More about the early history of library catalogs has been collected in 1956 by Strout.
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
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.
Currently, most cataloging rules are similar to, or even based on, the International Standard Bibliographic Description (ISBD), a set of rules produced by the International Federation of Library Associations (IFLA) to describe a wide range of library materials. These rules organize the bibliographic description of an item in the following areas: title and statement of responsibility (author or editor), edition, material-dependent information (for example, the scale of a map), publication and distribution, physical description (for example, number of pages), series, note, and standard number (ISBN). The most commonly used set of cataloging rules in the English speaking world are the Anglo-American Cataloging Rules, 2nd Edition, or AACR2 for short. In the German-speaking world there exists the Regeln für alphabetische Katalogisierung, abbreviated RAK. AACR2 has been translated into many languages, however, for use around the world. AACR2 provides rules for descriptive cataloging only and does not touch upon subject cataloging.
Library items that are written in a foreign script are, in some cases, transliterated to the script of the catalog.
In a title catalog, one can distinguish two sort orders:
The grammatic sort order has the advantage that often, the most important word of the title is also a good keyword (question 3), and it is the word most users remember first when their memory is incomplete. However, it has the disadvantage that many elaborate grammatic rules are needed, so that only expert users may be able to search the catalog without help from a librarian.
In some catalogs, person's names are standardized, i. e., the name of the person is always (catalogued and) sorted in a standard form, even if it appears differently in the library material. This standardization is achieved by a process called authority control. An advantage of the authority control is that it is easier to answer question 2 (which works of some author does the library have?). On the other hand, it may be more difficult to answer question 1 (does the library have some specific material?) if the material spells the author in a peculiar variant. For the cataloguer, it may incur (too) much work to check whether Smith, J. is Smith, John or Smith, Jack.
For some works, even the title can be standardized. The technical term for this is uniform title. For example, translations and reeditions are sometimes sorted under their original title. In many catalogs, parts of the Bible are sorted under the standard name of the book(s) they contain. The plays of William Shakespeare are another frequently cited example of the role played by a uniform title in the library catalog.
Many complications about alphabetic sorting of entries arise. Some examples:
For a fuller discussion, see collation.
In a subject catalog, one has to decide on which classification system to use. The cataloger will select appropriate subject headings for the bibliographic item and a unique classification number (sometimes known as a "call number") which is used not only for identification but also for the purposes of shelving, placing items with similar subjects near one another, which aids in browsing by library users, who are thus often able to take advantage of serendipity in their search process.
Online cataloging has greatly enhanced the usability of catalogs, thanks to the rise of MAchine Readable Cataloging = MARC standards in the 1960s. Rules governing the creation of catalog MARC records include not only formal cataloging rules like AACR2 but also special rules specific to MARC, available from the Library of Congress and also OCLC. MARC was originally used to automate the creation of physical catalog cards; Now the MARC computer files are accessed directly in the search process. OPACs have enhanced usability over traditional card formats because:
If you are looking for a book, or some other item, you can access the OPAC of your nearest library and search for it there. If you cannot find a particular book in the catalog, it may be obtainable through an interlibrary loan, also known to librarians as I.L.L. Ask the nearest Reference librarian for assistance.
If you want to see whether a book exists and you have few elements to identify it, you can use a meta-searcher: you can fill the query form once and spread your search over many library catalogues. A service such as MultiOpac does this task for you.