The Dewey Decimal Classification (DDC) system, created by
Melvil Dewey and first published in
1876, is the most commonly used library classification system in the world. About 95% of
public libraries and
public school libraries in the United States use the DDC. While the DDC is thought to not be sufficient for the fine level of detail needed for large academic libraries, which mostly use the
Library of Congress Classification System (LC), still about 20% of US college and university libraries employ it.
Structure
Dewey was a strong advocate of the
metric system and designed his classification system along those lines. The hierarchical structure of the DDC divides human knowledge into 10 broad classes based on academic disciplines or fields of study. Each of those classes is subdivided into 10 divisions, and each division is further divided into 10 sections. Further subdivisions are made as necessary.
The 10 main classes are:
000 -
Generalities
100 -
Philosophy & psychology
200 -
Religion
300 -
Social sciences
400 -
Language
500 -
Natural sciences & mathematics
600 -
Technology (Applied sciences)
700 -
The arts
800 -
Literature & Rhetoric
900 -
Geography & history
Follow the link for each class to find the divisions and sections.
As in every library classification system, each book is assigned a
call number. Each call number consists of a three-digit number denoting the class, division, and section. This number is followed by a
decimal point and more numbers indicating further subdivisions. For example, the field of
Euclidean geometry is assigned the number 516.372. This breaks down as follows:
500 Natural sciences and mathematics
510 Mathematics
516 Geometry
516.3 Analytic geometries
516.37 Metric differential geometries
516.372 Euclidean geometry
Often, the call number is followed by a
Cutter number or other form of author notation which distinguishes the book from other titles within the same specific field of study. The use of Cutter numbers, etc. is not limited to the DDC. The author notation is usually an arbitrary number referring to the alphabetical order of the name of the author, or sometimes the letters themselves are used.
Strengths
The proof is in the pudding: the DDC has survived a hundred years of intensive use and its popularity around the world proves that it fulfils its purpose. The metric-based hierarchical system is easy to learn, and children can master it while college educated adults often wander the stacks bewildered by the intricate LC classification system. One can master as much or as little of the DDC as one wants and still be able to navigate the stacks effectively. While it is inadequate for large research libraries, the DDC is probably ideal for the public library and general library patrons.
Weaknesses
The DDC is often accused of being
ethnocentric, and, well, it is. The fact that all non-Christian religions are dumped into the
290 section for "other" is proof enough. The design of other classes indicates a clear Anglo-American bias.
The rigid hierarchical system makes it difficult to
shoehorn in developing new fields of knowledge (say,
computers). The design is often nonsensical, as related disciplines are sometimes separated and unrelated disciples are combined, such as including
psychology under
philosophy in the
100s. The overall design represents the outmoded
world view of the 19th century.
History
Melvil Dewey designed the DDC in
1873 while working at the
Amherst College library. Traditionally, libraries had operated using the
fixed location method, where you stuck a book on the shelf and your catalog referred to where it was on the shelf. Dewey’s great innovation was to organize the books in relationship to one another, by their academic discipline and not by the accident of fate that led them to wherever they ended up on the shelf. It was a common system that could unify libraries, so you could look in the same relative location in different libraries and find the same book, previously an impossibility.
Dewey based the broad division of classes on a
1870 classification system devised by one W.T. Harris, who himself had based it upon the ideas of philosopher
Francis Bacon. Bacon divided human knowledge into three broad areas: history,
poesy, and philosophy. Harris subdivided those three areas into 12 areas, which Dewey narrowed to 10.
Dewey, who died in
1931, supervised revisions of the DDC up until the 13th. (The ever quirky Dewey was an advocate of simplifying the spelling of English, and published editions reflected his ideas, no doubt much to the frustration of librarians everywhere.) The 15th edition (
1951) was almost the last, as drastic changes in the structure and pruning of detailed subdivisions frustrated librarians. Faced with the task of a major overhaul of their catalogs and stacks, many librarians rejected the changes out of hand. Keeping the hard-learned lessons in mind, later revisions of the DDC and other classification systems came at a slower and more manageable pace, at the price of not being able to change as quickly as time and history does.
The DDC is currently in its 21st edition (
1996), with the 22nd to come in
2003. The DDC is currently maintained by the
Library of Congress and published by
Forest Press, a division of
OCLC.
The primary source (aside from library school and years of library use) is Cataloging and Classification by Lois Mai Chan, 1994.