The Dewey Decimal Classification (DDC), or Dewey Decimal System, is a proprietary library classification system created by Melvil Dewey in 1876. It has been revised and expanded through 23 major editions, the latest issued in 2011. Dewey was responsible for all revisions until his death in 1931. A designation number, such as Dewey 16 for the 16th edition, is given for each revision. A library assigns a DDC number that unambiguously locates a particular volume to within a short length of shelving which makes it easy to find any particular book and return it to its proper place on the library shelves. The system is used in 200,000 libraries in at least 135 countries.
Design The Dewey Decimal Classification is a system of library classification made up of ten classes, each divided into ten divisions, each having ten sections (although there are only 99 of 100 divisions and 908 of 999 sections in total, as some are no longer in use or have not been assigned). Just as in an alphanumeric system, the Dewey Decimal Classification is 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 the form of an item, rather than drawing upon a list containing each class and its meaning.
For example, 330 for economics + .9 for geographic treatment + .04 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 catalogued in ascending numerical order; when two or more books have the same classification number, the system sub-divides the class alphabetically, by the use of a call number (usually the first letter, or letters, of the author’s last name, or the title if there is no identifiable author).
The Dewey Decimal Classification has a number for all books, including fiction. Most libraries create a separate fiction section to allow shelving in a more generalized fashion than Dewey provides for, or to avoid the space that would be taken up in the 800s, or simply to allow readers to find preferred authors by alphabetical order of surname. Some parts of the classification offer options to accommodate different kinds of libraries.
An important feature of the scheme is the ability to assign multiple class numbers to a bibliographical item and only use one of them for shelving. The added numbers appear in the classified subject catalog (though this is not the usual practice in North America). For the full benefit of the scheme the relative index and the tables that form part of every edition must be understood and consulted when required. The structure of the schedules is such that subjects close to each other in a dictionary catalog are dispersed in the Dewey schedules (for example, architecture of Chicago quite separate from geography of Chicago).