Library classification

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A library classification is a system of coding and organizing library materials (books, serials, audiovisual materials, computer files, maps, manuscripts, realia) according to their subject and allocating a call number to that information resource. Similar to classification systems used in biology, bibliographic classification systems group entities that are similar together typically arranged in a hierarchical tree structure (assuming none-faceted system).

Library classification forms part of the field of library and information science. It goes hand in hand 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 are alphabetical indexing languages such as Thesaurui and Subject Headings systems.

In the United States, academic libraries generally use the Library of Congress classification system and public and school libraries use the Dewey Decimal Classification System.



Classification of a piece of work consists of two steps. Firstly the 'aboutness' of the material is ascertained. Next, a call number based on the classification system will be assigned to the work using the notation of the system.

It is important to note that unlike subject heading or Thesaurui where multiple terms can be assigned to the same work, in classification systems, each work can only be placed in one class. This is true also for faceted (see later) classification systems due to the enforcement of a citation order. Most classification systems like DDC and Library of Congress classification, also add a "cutter number" to each work which adds a code for the author of the work.

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. Secondly, they provide a known location for the information source to be located (e.g where it is shelved).

Until the nineteenth century, most libraries had closed stacks, so the library classification only served to organize the subject catalog. In the twentieth century, libraries opened their stacks to the public and started to shelve the 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, UDC which uses a complicated notation including plus, colons are more difficult to use for the purpose of shelf arrangement but are 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.

In the United States, academic libraries generally use Library of Congress classification system and public and school libraries use Dewey Decimal Classification System.


There are many standard systems of library classification in use, and many more have been proposed over the years. However in general, Classification systems can be divided into three types depending on how they are used.

  • Universal schemes covering all subjects. Examples include Dewey Decimal Classification and Library of Congress Classification
  • Specific classification schemes. Examples includes Iconclass, British classification of Music
  • National schemes specially created for certain countries. Example is SAB.

In terms of functionality, classification systems are often described as

  • enumerative: produce an alphabetical list of subject headings, assign numbers to each heading in alphabetical order
  • hierarchical: divides subjects hierarchically, from most general to most specific
  • faceted or analytico-synthetic: divides subjects into mutually exclusive orthogonal facets

There are few completely enumerative systems or faceted systems, most systems are a blend but favouring one type or the other. The most common classification systems, LCC and DDC, are essentially enumerative, though with some hierarchical and faceted elements (more so for DDC), especially at the broadest and most general level. The first true faceted system was the Colon classification of S. R. Ranganathan.

Specific classification systems used in English-speaking world

  • Bliss bibliographic classification (BC)
  • Dewey Decimal Classification (DDC)
  • Library of Congress Classification (LC)
  • Dickinson classification

(The above systems are the most common in the English-speaking world.)

  • Harvard-Yenching Classification - An English classification system for Chinese language materials.

Specific classification systems in other languages

  • Nippon Decimal Classification (NDC)
  • Chinese Library Classification (CLC)
  • Korean Decimal Classification (KDC)

Specific classification systems that rely on synthesis (faceted systems)

  • Bliss bibliographic classification
  • Colon classification
  • Cutter Expansive Classification
  • Universal Decimal Classification
  • Brinkler classification

Newer classification systems tend to use the principle of synthesis (combining codes from different lists to represent the different attributes of a work) heavily, which is comparatively lacking in LC or DDC.

Comparing Classification Systems

As a result of differences in Notation, history, use of enumeration, hierarchy , facets, classification systems can differ in the following ways

  • Type of Notation - Notation can be pure (consisting of only numerals for example) or mixed (consisting of both alphabets and numerals or other symbols).
  • Expressiveness - This is the degree in which the notation can express relationship between concepts or structure.
  • Whether they support mnemonics - For example the number 44 in DDC notation usually means it concerns some aspect of France. For example 598.0944 concerns "Birds in France." The 09 signifies country code, and 44 represents France.
  • Hospitality - The degree in which the system is able to accommodates new subjects
  • Brevity - Length of the notation to express the same concept
  • Speed of updates and degree of support - The best classification systems are constantly being reviewed and improved.
  • Consistency
  • Simplicity

Library of Congress Classification System

Library of Congress reading room

The Library of Congress Classification (LCC) is a system of library classification developed by the Library of Congress. It is used by most research and academic libraries in the U.S. and several other countries—most public libraries and small academic libraries continue to use the Dewey Decimal Classification (DDC). It is not to be confused with the Library of Congress Subject Headings or Library of Congress Control Number.

The classification was originally developed by Herbert Putnam with the advice of Charles Ammi Cutter in 1897 before he assumed the librarianship of Congress. It was influenced by Cutter Expansive Classification, DDC, and was designed for the use by the Library of Congress. The new system replaced a fixed location system developed by Thomas Jefferson. By the time of Putnam's departure from his post in 1939 all the classes except K (Law) and parts of B (Philosophy and Religion) were well developed. It has been criticized as lacking a sound theoretical basis; many of the classification decisions were driven by the particular practical needs of that library, rather than considerations of epistemological elegance.

Although it divides subjects into broad categories, it is essentially enumerative in nature. It provides a guide to the books actually in the library, not a classification of the world.

The National Library of Medicine classification system (NLM) uses unused letters W and QS-QZ. Some libraries use NLM in conjunction with LCC, eschewing LCC's R (Medicine).

The system

Letter Subject area
A General Works
B Philosophy, Psychology, and Religion
C Auxiliary Sciences of History
D General and Old World History
E History of America
F History of the United States and British, Dutch, French, and Latin America
G Geography, Anthropology, and Recreation
H Social Sciences
J Political Science
K Law
L Education
M Music
N Fine Arts
P Language and Literature
Q Science
R Medicine
S Agriculture
T Technology
U Military Science
V Naval Science
Z Bibliography, Library Science, and General Information Resources

Library of Congress Subject Headings

The Library of Congress Subject Headings (LCSH) comprise a thesaurus (in the information technology sense) of subject headings, maintained by the United States Library of Congress, for use in bibliographic records. LC Subject Headings are an integral part of bibliographic control, which is the function by which libraries collect, organize and disseminate documents. LCSHs are applied to every item within a library’s collection, and facilitate a user’s access to items in the catalogue that pertain to similar subject matter. If users could only locate items by ‘title’ or other descriptive fields, such as ‘author’ or ‘publisher’, they would have to expend an enormous amount of time searching for items of related subject matter, and undoubtedly miss locating many items because of the ineffective and inefficient search capability.

An art and science

Subject heading classification is a human and intellectual endeavor, where trained professionals apply topic descriptions to items in their collections. Naturally, every library may choose to categorize the subject matter of their items differently, without a uniform agreed upon standard. The widespread use and acceptance of the Library of Congress Subject Headings facilitates the uniform access and retrieval of items in any library in the world using the same search strategy and LCSH thesaurus, if the correct headings have been applied to the item by the library. Thusly, LCSH decisions involve a great amount of debate and even controversy in the library community.

Despite LCSH's wide-ranging and comprehensive scope, there are libraries where the use of LCSH is not ideal or effective. To deal with these types of collections and user communities, other subject headings may be required. The United States National Library of Medicine developed Medical Subject Headings (MeSH) to use on its many health science databases and collection. Many university libraries may apply both LCSH and MeSH headings to items. In Canada, the National Library of Canada worked with LCSH representatives to create a complementary set of Canadian Subject Headings (CSH) to access and express the topic content of documents on Canada and Canadian topics.

LCSH policy issues

Historically, issues have revolved around the terms employed to describe racial or ethnic groups. Notable has been the terms used to describe African-Americans. Until the 1990s, the LCSH administrators had a strict policy of not changing terms for a subject category. This was enforced to tighten and eliminate the duplication or confusion that might arise if subject headings were changed. Therefore, one term to describe African-American topics in LCSH was ‘Afro-American’ long after that term lost currency and acceptance in the population. LCSH decided to allow some alteration of terms in 1996 to better reflect the needs and access of library users. Nevertheless, many common terms, or ‘natural language’ terms are not used in LCSH, and may in effect limit the ability for users to locate items. There is a vibrant, interesting and growing tradition of research in Library and Information Science faculties about the cultural and gender biases that affect the terms used in LCSH, which in turn may limit or deprive library users access to information stored and disseminated in collections. A notable American Library Science scholar on this subject is Sanford Berman.

Using LCSH

The Subject Headings are published in large red volumes (currently five), which are typically displayed in the reference sections of research libraries. They may also be searched online in the Library of Congress Classification Web</ref>Library of Congress Classification Web, Library of Congress. Retrieved April 4, 2008.</ref> a subscription service, or free of charge at Library of Congress Authorities[1] The Library of Congress issues weekly updates. Once a library user has found the right subject heading they are an excellent resource for finding relevant material in your library catalogue. Increasingly the use of hyperlinked, web-based Online Public Access Catalogues, or OPACs, allow users to hyperlink to a list of similar items displayed by LCSH once one item of interest is located. However, because LCSH are not necessarily expressed in natural language, many users may chose to search OPACs by keywords. Moreover, users unfamiliar with OPAC searching and LCSH, may incorrectly assume their library has no items on their desired topic, if they chose to search by ‘subject’ field, and the terms they entered do not strictly conform to a LCSH. For example ‘body temperature regulation’ is used in place of ‘thermoregulation’. Thus the easiest way to find and use LCSH is to start with a ‘keyword’ search and then look at the Subject Headings of a relevant item to locate other related material.


Despite their limitations, LCSH are widely used in library catalogs in North America and around the world. They should not be confused with the Library of Congress Classification, which does not attempt to evaluate the subject content of items, but rather broadly categorizes the item in a subject hierarchy. Many libraries, especially public and school libraries will use the Dewey Decimal Classification system for organizing collections, but will employ LCSH for accessing material by topic.

Dewey Decimal Classification System

The Dewey Decimal Classification (DDC, also called the Dewey Decimal System) is a proprietary system of library classification developed by Melvil Dewey in 1876, and has since then been greatly modified and expanded through 22 major revisions, the most recent in 2004.

How it works

The DDC attempts to organize all knowledge into ten main classes. The ten main classes are then further subdivided. Each main class has ten divisions, and each division has ten sections. Hence the system can be summarized in 10 main classes, 100 divisions and 1,000 sections. DDC's advantage in choosing decimals for its categories allows it to be both purely numerical and infinitely hierarchical.

It also uses some aspects of a faceted classification scheme, combining elements from different parts of the structure to construct a number representing the subject content (often combining two subject elements with linking numbers and geographical and temporal elements) and form of an item rather than drawing upon a list containing each class and its meaning.

Except for general works and fiction, works are classified principally by subject, with extensions for subject relationships, place, time or type of material, producing classification numbers of not less than three digits but otherwise of indeterminate length with a decimal point before the fourth digit, where present (e.g. 330 for economics + 9 for geographic treatment + 4 for Europe = 330.94 European economy; 973 for United States + 05 form division for periodicals = 973.05, periodicals concerning the United States generally).

Books are placed on the shelf in increasing numerical order; the whole number to the left of the decimal is in counting order, while the digits to the right of the decimal are compared one digit at a time, with a blank coming before zero. (Example: 050, 220, 330.973, 331 etc.) When two books have the same subject, and therefore the same classification number, the second line of the call number, which usually has the first letter or first several letters of the author's last name (or the title if there is no identifiable author), is placed in alphabetical order.

It is a common misconception that all books in the DDC are non-fiction. The DDC has a number for all books, including those that generally become their own section of fiction. If DDC rules are strictly followed, American fiction is classified in 813. Most libraries create a separate fiction section to allow shelving fiction in a more generalised fashion than Dewey provides for, or to avoid the space that would be taken up in the 800s.

DDC compared to other classification systems

DDC's numbers formed the basis of the more expressive but complex Universal Decimal Classification, which combines the basic Dewey numbers with selected punctuation marks (comma, colon, parentheses etc.). Besides its frequent revision, DDC's main advantage over its chief rival—the Library of Congress Classification system developed shortly afterward—is its simplicity. Thanks to the use of pure notation, a mnemonics system and a hierarchical decimal place system, it is generally easier to use for most users.

DDC and UDC are also more flexible than Library of Congress Classification because of greater use of facets (via auxiliary tables) while Library of Congress Classification is almost totally enumerative.

On the flip side, DDC's decimal system means that it is less hospitable to the addition of new subjects, as opposed to Library of Congress Classification which has 21 classes at the top level. Another side effect of this is that DDC notations can be very much longer compared to the equivalent class in other classification systems.

Another disadvantage of DDC is that it was developed in the nineteenth century, by essentially one man, and was built on a top down approach to classify all human knowledge which made it difficult to adapt to changing fields of knowledge. In contrast, the Library of Congress Classification system was developed based mainly on the idea of literary warrant; classes were added (by individual experts in each area) only when needed for works owned by the Library of Congress. As a result, while the Library of Congress Classification system was able to incorporate changes and additions of new branches of knowledge, particularly in the fields of engineering and computer science (the greater hospitality of the Library of Congress Classification was also a factor), DDC has been criticized for being inadequate for covering those areas. As a result, most major academic libraries in the US do not use the DDC because the classification of works in those areas is not specific enough.

The Library of Congress Classification system is not without problems; because each area is developed by an expert according to demands of cataloging, there is little consistency. It is also highly US-centric (more so than DDC) because of the nature of the system, and compared to DDC and UDC it has been translated into far fewer languages.

Ownership and administration

The Online Computer Library Center of Dublin, Ohio, acquired the trademark and any copyrights associated with the Dewey Decimal System when it bought Forest Press in 1988. OCLC maintains the classification system and publishes new editions of the system. The work of assigning a DDC number to each newly published book is performed by a division of the Library of Congress, whose recommended assignments are either accepted or rejected by the OCLC after review by an advisory board; to date all have been accepted.

In September 2003, the OCLC sued the Library Hotel for trademark infringement. The settlement was that the OCLC would allow the Library Hotel to use the system in its hotel and marketing. In exchange, the Hotel would acknowledge the Center's ownership of the trademark and make a donation to a nonprofit organization promoting reading and literacy among children.


The system is made up of ten main classes or categories, each divided into ten secondary classes or subcategories, each having ten subdivisions of its own. For a more detailed list, see List of Dewey Decimal classes.


  • Buchanan, Brian. Theory of Library Classification. Outlines of modern librarianship. London: C. Bingley, 1979. ISBN 0851572707 ISBN 9780851572703
  • Dewey, Melvil, et al. Dewey Decimal Classification and Relative Index. Albany, New York: Forest Press, a division of OCLC Online Computer Library Center, 1989. ISBN 0910608377 ISBN 9780910608374
  • LaMontagne, Leo E. American Library Classification: With Special Reference to the Library of Congress. Hamden, Conn: Shoe String Press, 1961.
  • Library of Congress. Library of Congress Classification. T. Technology. Washington, D.C.: Library of Congress, Cataloging Distribution Service, 2007. ISBN 0844411647 ISBN 9780844411644
  • Library of Congress. Library of Congress Subject Headings. Washington: Library of Congress, 1975. Library of Congress. Subject Cataloging Manual. Classification. Washington, D.C.: Cataloging Distribution Service, Library of Congress, 1992.
  • World Council of Churches. Library Classification. Geneva: WCC Library, 1971.
  • Wynar, Bohdan S., Arlene G. Taylor, and Jeanne Osborn. Introduction to Cataloging and Classification. Library science text series. Littleton, Colo: Libraries Unlimited, 1980. ISBN 0872872203 ISBN 9780872872202 ISBN 0872872211 ISBN 9780872872219

External links

Library of Congress Classification

Dewey Classification


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