Dewey Decimal

The Dewey Decimal system is the granddaddy of them all. Developed in 1873, and now in its 22nd edition, its ease of use has made it a favorite of public libraries and media centers everywhere. In fact, many classification systems used outside of the United States, such as Universal Decimal Classification and Nippon Decimal Classification, have their roots in Dewey.

The Dewey Decimal system, or DDC, is set up, at its core, as a branching hierarchy, sort of like a family tree. "The library is first divided into nine special libraries which are called Classes" (Dewey 1876, Preface, para. 1). Each of these represents a massive category of human knowledge which is represented by a digit from 1 to 9. For instance, "5" represents the Natural Sciences, while a "9" means History. The tenth (or first, depending on how you look at things) set, the "0's," originally contained general reference works such as dictionaries and encyclopedias, and books about libraries proper. Since its advent, computer science, too, is contained in this null category.

The aforementioned class makes up the first digit of a DDC filing number. Each class is then further stratified into Divisions, which are, in turn, divided into Sections, each of which is assigned a digit from 0-9. "Thus 513 is the 3d Section (Geometry) of the 1st Division (Mathematics) of the 5th Class (Natural Science). This number, giving Class, Division, and Section, is called the Classification or Class Number, and is applied to every book or pamphlet belonging to the library" (Dewey 1876, Preface, para. 1).

This classification can go even deeper by introducing a decimal point and continuing to introduce new sets of 10 subdivisions. This can get almost painfully long (for instance, horses are 599.6655), but this allows for a remarkable amount of fine-tuning. One can even use the system to build new numbers using Tables. For example, "0901" can be tacked on the end of any Dewey number to indicate a time period of "to 499 A.D." So card games, which are classified under 795.4, can become 795.40901 to indicate ancient card games. Again, cumbersome, but really, really cool.

Anyway, the system isn't perfect. As said above, the numbers can get really unwieldy. In addition, while the revisions have introduced new categories to better classify modern stuff, the structure itself is immutable, and mired in the worldview of a 19th century New Englander. For instance, the 200's cover Religion. In there, 200-220 cover general philosophical theses on religion, 220-290 cover the Bible and Christianity, and every other religion on Earth is crammed into the 290's. This isn't as much of a problem as it might seem, since the numbers can be extended infinitely, but it is still inconvenient and embarassing.

Despite these warts, though, the DDC remains easy to use and convenient. If you know the Classes, you can even begin your search without the help of a catalog. Pretty neat, huh?

Sources:

Dewey, M. (1876). A classification and subject index for cataloging and arranging the books and pamphlets of a library [Electronic version]. Kingsport, Tenn.: Kingsport Press.

WebDewey. Accessed through connexion.oclc.org.