Library classification systems

Up to the 19th century, many libraries simply arranged their books by size and date of acquisition. Individual books could be found through a catalogue. Others used simple classifications. Increasing public access and size led to the introduction of various more sophisticated library classification systems, of which some important or distinctive ones are briefly covered below.

Decimal classification (1st edition, Melvil Dewey, 1876; 23rd edition, 4 volumes, Online Computer Library Center, 2011)

This system is distinctive in its use of numerals for top-level classes, as most use letters. These are as follows:

• 100 Philosophy and psychology
• 200 Religion
• 300 Social sciences
• 400 Language
• 500 Pure science
• 600 Technology
• 700 Arts and recreation
• 800 Literature
• 900 History and geography

Further subdivisions are made by adding digits in place of zeros: 510 mathematics, 423 English dictionaries etc. Beyond this, decimal points are used: 794.1 chess etc. Books of a more general nature are not so subdivided, but have their own subdivisions: 033 German encyclopaedias, 501 philosophy of science etc.

There is no specification for the order of books within the lowest levels of classification. Libraries generally arrange books alphabetically by author. Order of books by the same author is variously by title, date or size in different libraries.

This system is used in most libraries in the English-speaking world. Note, however, that it is used, not followed. In particular, it is usually ignored for fiction, which it would distribute among various national literatures: 813 American fiction, 823 British fiction etc. Most libraries put all fiction in English (including translations from other languages) in alphabetical sequence outside the classification.

There is a "fork" of this system called the Universal Decimal Classification, originated in Belgium. It drops trailing zeros and incorporates language with literature, so that 8 covers literature and language.

Expansive classification (Charles Ammi Cutter, 1891-1903)

Cutter was responding to complaints by custodians of small libraries that systems such as the decimal classification were too complicated for their purposes. The expansive classification is in fact a series of seven classifications for libraries of different sizes, the last of which was not quite finished by the time of Cutter's death. Libraries with some degree of specialization might use different levels in different fields. The lowest level has just eight classes. Cutter gives two versions of this in his book of the first six levels, in the introduction and main body. Possibly he revised one but forgot to revise the other. These are as follows:

• A Reference and general (Cutter regards Reference as a "form" class like literature, generally characterized by alphabetical arrangement)
• B Philosophy and religion
• E Historical sciences, or subdivided:
  • E Biography
  • F History and geography and travels
• H Social sciences
• L Natural sciences and arts
• Y Language and literature, or subdivided:
  • X Language
  • Y Literature
• YF Fiction

TBC