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About Universal Decimal Classification
Summary of classification | UDC Consortium
What is the UDC?
The Universal Decimal Classification (UDC) is the world's foremost multilingual classification scheme for all fields of knowledge, a sophisticated indexing and retrieval tool. It was adapted by Paul Otlet (Rayward's Otlet page; Wikipedia entry ) and Nobel Prizewinner Henri La Fontaine from the Decimal Classification of Melvil Dewey, and first published (in French) between 1904 and 1907. Since then, it has been extensively revised and developed, and has become a highly flexible and effective system for organizing bibliographic records for all kinds of information in any medium (it is well suited to multi-media information collections). It is structured in such a way that new developments and new fields of knowledge can be readily incorporated. The code itself is independent of any particular language or script (consisting of arabic numerals and common punctuation marks), and the accompanying class descriptions have appeared in many translated versions. UDC is in worldwide use, and has been published in whole or in part in 40 different languages (see bibliography of UDC editions).
UDC is used in bibliographic services, documentation centres and libraries in around 130 countries world-wide (see an overview). Library collections indexed by UDC can be found in library OPACs and databases (see information about larger collections).
The International Federation for Information and Documentation (FID) managed UDC from its creation around 1900 until the 1980s when it became clear that a more broadly based and financially autonomous organization was needed to administer and exploit UDC. FID, together with the publishers of the Dutch, English, French, Japanese and Spanish editions, became the founder members of a new body: the UDC Consortium (UDCC). The Consortium assumed ownership of UDC on 1 January 1992. The UDCC appoints the UDC Editorial Team and an Advisory Board with international membership, to oversee the content of UDC and contribute to its revision.
Scope
All branches of human knowledge have a place in UDC, and are treated as parts of a balanced whole. Because of the nature of the subjects, the listed subdivisions in science and technology outweigh those of the arts and social sciences, but these subjects demand different criteria, and are also properly provided for. UDC has been modified and extended over many years to cope with the increasing output in all disciplines, and is still under continuous review so as to take account of new developments.
Structure
UDC’s most innovative and influential feature is its ability to express not just simple subjects but relations between subjects. This facility is added to a hierarchic structure, in which knowledge is divided into ten classes, then each class is subdivided into its logical parts, each subdivision is further subdivided, and so on. The more detailed the subdivision, the longer the number that represents it. This is made possible by the decimal notation (see ‘Notation and arrangement’ below).
In UDC, the universe of information (all recorded knowledge) is treated as a coherent system, built of related parts, in contrast to a specialised classification, in which related subjects are treated as subsidiary even though in their own right they may be of major importance. Thus specialists may often be led to related information of which they would otherwise have been unaware.
Notation and arrangement
The symbols chosen for UDC notation are non-language-dependent, and universally recognizable - the arabic numerals, supplemented by a few other signs familiar from mathematics and ordinary punctuation. They are not only easily readable, but easily transcribable using ordinary office machinery such as typewriters and computer keyboards.
The arrangement is based on the decimal system: every number is thought of as a decimal fraction with the initial point omitted, and this determines the filing order, but, for ease of reading, it is usually punctuated after every third digit. Thus, after 61 'Medical sciences' come the subdivisions 61 1 to 61 9; under 61 1 'Anatomy' come its subdivisions 61 1.1 to 61 1.9; under 61 1.1 come all of its subdivisions before 611.2 occurs, and so on; after 619 comes 62. An advantage of this system is that it is infinitely extensible, and when new subdivisions are introduced, they need not disturb the existing allocation of numbers.
The Tables
There are two kinds of tables in UDC:
- The main tables (also called the 'schedules'): these contain the outline of the various disciplines of knowledge, arranged in 10 classes and hierarchically divided (as explained in 'Structure' above). They are numbered from 0 to 9.
- Auxiliary tables (also called 'common auxiliary tables'), including certain auxiliary signs. The signs (e.g. the plus, the stroke, the colon) are used to link two (or more) numbers, so expressing relations of various kinds between two (or more) subjects. The enumerative tables denote recurrent characteristics, applicable over a range of subjects; the auxiliary is simply added at the end of the number for the subject. The most general of them, called common auxiliaries, are applicable throughout the main tables, and represent notions such as place, language of the text and physical form of the document, which may occur in almost any subject. There are also more restricted series, called special auxiliaries, which express aspects that are recurrent, but in a more limited subject range. They are therefore listed only in particular sections of the main tables.
Maintenance
A core version of UDC, with more than 68,000 subdivisions, is mantained in the UDC Master Reference File database and the standard UDC scheme is distributed in English, as a database file export called the UDC MRF under various licences. Although the main language of the database is English, a great proportion of data exists in parallel in German and Dutch and will be fully aligned with the English language data by 2012 (see also UDC Summary - a freely available mulgiliangual selection of the scheme).UDC MRF updates have been released annually since 1993.
In the period 2007-2009 the UDC MRF database was migrated to a new mySQL database with many added features including an enhanced data structure for UDC content management and access.
Since 1992 the UDC Consortium has maintained the quality of the scheme by reviewing its content and initiating revisions and extensions. Since 1993 approximately 40% of UDC scheme has been completely revised and updated. The results are published in the journal Extensions and Corrections to the UDC (ISSN 0014-5424) which also contains articles and major revision proposals. Editions of UDC, incorporating the authorized amendments, are published by the members of the Consortium, each in its own language and by many other licensed publishers.
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