Editing Library classification (section)

==The practice of classifying==

Library classification is associated with library (descriptive) cataloging under the rubric of ''cataloging and classification'', sometimes grouped together as ''technical services''. The library professional who engages in the process of cataloging and classifying library materials is called a ''cataloger'' or ''catalog librarian''. Library classification systems are one of the two tools used to facilitate [[subject access]].  The other consists of alphabetical indexing languages such as Thesauri and Subject Headings systems.

The practice of library classification is a form of the more general task of [[classification]]. The work consists of two steps. Firstly, the subject or topic of the material is ascertained. Next, a '''call number''' (essentially a book's address) based on the classification system in use at the particular library will be assigned to the work using the notation of the system.

Unlike subject heading or thesauri where multiple terms can be assigned to the same work, in library classification systems, each work can only be placed in one class. This is due to shelving purposes: A book can have only one physical place. However, in classified catalogs one may have main entries as well as added entries. Most classification systems like the [[Dewey Decimal Classification]] (DDC) and [[Library of Congress Classification]] also add a [[cutter number]] to each work which adds a code for the main entry (primary access point) of the work (e.g. author).

Classification systems in libraries generally play two roles. Firstly, they facilitate [[subject access]] by allowing the user to find out what works or documents the library has on a certain subject.<ref>{{cite web|url=http://www.iva.dk/bh/lifeboat_ko/concepts/subject_access_points.htm|title=Subject access points|work=iva.dk|access-date=2011-02-16|archive-url=https://web.archive.org/web/20110531001950/http://www.iva.dk/bh/lifeboat_ko/CONCEPTS/subject_access_points.htm|archive-date=2011-05-31|url-status=dead}}</ref> Secondly, they provide a known location for the information source to be located (e.g. where it is shelved).

Until the 19th century, most libraries had closed stacks, so the library classification only served to organize the subject [[library catalog|catalog]]. In the 20th century, libraries opened their stacks to the public and started to shelve library material itself according to some library classification to simplify subject browsing.

Some classification systems are more suitable for aiding subject access, rather than for shelf location. For example, [[Universal Decimal Classification]], which uses a complicated notation of pluses and colons, is more difficult to use for the purpose of shelf arrangement but is more expressive compared to DDC in terms of showing relationships between subjects. Similarly [[faceted classification]] schemes are more difficult to use for shelf arrangement, unless the user has knowledge of the citation order.

Depending on the size of the library collection, some libraries might use classification systems solely for one purpose or the other. In extreme cases, a public library with a small collection might just use a classification system for location of resources but might not use a complicated subject classification system. Instead all resources might just be put into a couple of wide classes (travel, crime, magazines etc.). This is known as a "mark and park" classification method, more formally called reader interest classification.<ref>Lynch, Sarah N., and Eugene Mulero. [https://www.nytimes.com/2007/07/14/us/14dewey.html "Dewey? At This Library With a Very Different Outlook, They Don't"] ''[[The New York Times]]'', July 14, 2007.</ref>