The Dewey Decimal Classification (DDC, also called the Dewey Decimal System) is a system of library classification developed by Melvil Dewey (1851–1931) in 1876, and since greatly modified and expanded in the course of the twenty-two major revisions which have occurred up until 2004.

DDC's cleverness is in choosing decimals for its categories; this allows it to be both purely numerical while infinitely hierarchical. It also is a faceted classification, 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 economy + 94 for Europe = 330.94 European economy; 973 for United States + 005 form division for periodicals = 973.005, periodicals concerning the United States generally); classmarks are to be read as numbers, in the order: 050, 220, 330.973, 331 etc. Any letter should be read as preceding any number that might have occupied the same character position, so "330.94 A" would come before 330.943. The system uses ten main classes, which are then further subdivided. It is a common misconception that all books in the DDS are non-fiction. However, the DDS has a number for all books, including those that generally become their own section of fiction. If DDS rules were strictly followed, fiction would be classified in 813. Most libraries create a separate fiction section because of the space that would be taken up in the 813s.

DDC is commonly used in public and school libraries throughout the world. The schedule contains marked geographical biases derived from its 19th century origins: Northern Africa for instance occupies all of 961–965, the rest of the continent only 966–969. It is still more biased towards Christianity against other religions, the former covering all of 200–289, while all others get only 290–299 to share. Recent versions permit another religion to be placed in 200–289, with Christianity relegated to 290–299, but this is mainly used by libraries operated by non-Christian religious groups, especially Jewish ones.

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.). Despite its frequent revision, DDC is widely considered theoretically inferior to other more modern systems which make freer use of alphabetical characters to produce shorter classmarks for concepts of equal complexity, though it continues to offer a more expressive format than the Library of Congress Classification developed shortly afterward.

Main Classes

The system is made of up ten categories:

• 000 Computers, information and general reference
• 100 Philosophy and psychology
• 200 Religion
• 300 Social sciences
• 400 Language
• 500 Science and mathematics
• 600 Technology
• 700 Arts and recreation
• 800 Literature
• 900 History and geography

Ownership

The Online Computer Library Center acquired the trademark and any copyrights associated with the Dewey Decimal System when it bought Forest Press in 1988. OCLC classifies new books and maintains the classification system. 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.

Trivia

According to legend, Isaac Asimov is the only person to have authored a book in each of the Dewey Decimal System's ten main classes (listed above).

External links

• OCLC's Dewey Decimal website (http://www.oclc.org/dewey/)
• Full text of A Classification and Subject Index for Cataloguing and Arranging the Books and Pamphlets of a Library (Dewey Decimal Classification) (http://www.gutenberg.net/etext/12513) (1876) from Project Gutenberg