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About Universal Decimal Classification and the UDC Consortium
Summary of classification | Outline of the UDC
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 (1), (2), (3) and Nobel Prizewinner Henri La Fontaine from the Decimal Classification of Melvil Dewey, and first published (in French) from 1904 to 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 23 different languages. The English-language editions are extensively used both in anglophone countries and those where English is co-official or a working language (the British Isles, Canada, Australia, New Zealand, India, several African countries) and have a significant presence in other cultures as well.
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, 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.
UDC and computers
UDC works extremely well with computers, as it did with earlier automatic sorting devices. Scrolling through an on-screen display in classified order makes for productive browsing; and UDC's distinctive symbols make it possible to perform searches for any part of a compound number or for specified combinations of symbols, so providing highly accurate subject retrieval. UDC's combination of numerical codes and natural-language descriptions makes it amenable to numerical and alphabetic sorting, in maintaining tools such as catalogues, authority files and indexes. Both keepers and users of information sources are well served by UDC.
Maintenance
A core version of UDC (Master Reference File), with more than 65 000 subdivisions, is now available in database format. Since 1992 the UDC Consortium has maintained the quality of the scheme by reviewing its content and initiating revisions and extensions. The results are published in the journal Extensions and Corrections to the UDC, 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, or possibly by other licensed publishers.
Extensions and Corrections to the UDC is published annually by the UDC Consortium, normally in November.
The UDC Consortium
The International Federation for Information and Documentation (FID) was founded to manage UDC and had performed that function since its origin around 1900. But during the 1980s, it became clear that a more broadly based, and financially autonomous, organization was needed to administer and exploit UDC, and FID together with the publishers of the Dutch, English, French, Japanese and Spanish editions became founder members of a new body, the UDC Consortium (UDCC). The Consortium assumed ownership of UDC on 1 January 1992. One of its first actions was to create an international database which could be the source of many kinds of UDC edition. It is called the Master Reference File (MRF), and is held at the Royal Library in the Hague, and updated once a year. The UDCC has also appointed an Editor in Chief and an Advisory Board with international membership, to oversee the content of UDC and contribute to its revision.
UDC and the future
UDC has always been a major international scheme, but now that the UDCC has created an international (and eventually multilingual) database, it can be developed with the maximum of consistency and efficiency, and is more than ever the reflection of an authoritative international consensus. In the last few years, UDC has proved its value for organizing and searching electronic information, in several experimental projects. Licensing agreements are available (and several are in force) for the use of the MRF, e.g. on local area networks (LANs) from UDC Consortium. UDC in electronic form is also available on the web and licence can be purchased from British Standard Institution - UDC Online. There are electronic versions of the UDC available on CD ROM and these are published also in Spanish and Czech languages (see UDC publications).
Guide to use
The Universal Decimal Classification: a guide to its use by I.C. McIlwaine describes the overall structure of UDC, the underlying principles and the practical implementation of the theory. It is packed with practical examples, and explains how the classification can be applied and for what major purposes it can be used, both in traditional environments and in online applications.
Information about UDC (including editions in various languages) is available from:
UDC Consortium
PO Box 90407
2509 LK The Hague
The Netherlands
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