Dewey Decimal System

The Dewey Decimal Classification (DDC, also called the Dewey Decimal System) is a system of library classification developed by Melvil Dewey in 1876, and since greatly modified and expanded in the course of the twenty-two major revisions, the most recent in 2004.
The DDC attempts to organize all knowledge into ten main classes that, excluding the first class (000 Computers, information and general reference), proceed from the divine (philosophy & religion) to the mundane (history & geography). DDC's cleverness is in choosing decimals for its categories; this allows it to be both purely numerical and 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 economics + 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. Each main class has ten divisions and each division has ten sections. Hence the system can be neatly summarized in 10 main classes, 100 divisions and 1000 sections. It is a common misconception that all books in the DDC are non-fiction. However, 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. Some libraries create a separate fiction section because of the space that would be taken up in the 800s.

DDC is commonly used in public and school libraries throughout the world, although some college and university libraries of all sizes also use Dewey, notably Duke University and Northwestern University. 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 220–289, while all others get only 292–299 to share. Recent versions permit another religion to be placed in 220–289, with Christianity relegated to 298, but this is mainly used by libraries operated by non-Christian religious groups, especially Jewish ones. The DDC has also been criticized for its treatment of literature (800). Because primacy is given to language, national literatures get scattered. For example, Canadian literature in English is classed under English & Old English (820) literatures while Canadian literature in French is classed under French literatures (840). The only exception is for American literature (810); a reflection of the Anglo-American bias inherent in the system.