UDC Structure & Tables

Principle of Organization

The organization of knowledge in UDC is discipline-based. This means that concepts are subsumed and placed in the field under which they are studied. This particular feature is usually implemented in UDC by re-using the same concept in various combinations with the main subject, e.g. a code for language in common auxiliaries of language is used to derive numbers for ethnic grouping, individual languages in linguistics and individual literatures. Or, a code from the auxiliaries of place, e.g. (410) United Kingdom, uniquely representing the concept of United Kingdom can be used to express 911(410) Regional geography of United Kingdom and 94(410) History of United Kingdom.

UDC Hierarchic 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 UDC notational system).

5Mathematics. Natural sciences
539Physical nature of matter
539.1Nuclear physics. Atomic physics. Molecular physics
539.12Elementary and simple particles (charge less than 3)
539.120Theoretical problems of elementary particles physics
539.120.8Strong interaction, including experiments
539.120.81Quantum chromodynamics
539.120.811Lattice QCD

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.

UDC Tables

There are two kinds of tables in UDC:

1. 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.

0Science and Knowledge. Organization. Computer Science. Information Science. Documentation. Librarianship. Institutions. Publications
1Philosophy. Psychology
2Religion. Theology
3Social Sciences
5Mathematics. Natural Sciences
6Applied Sciences. Medicine, Technology
7The Arts. Entertainment. Sport
8Linguistics. Literature
9Geography. History

Each main UDC class may also contain tables called special auxiliaries (or special auxiliary numbers), which express aspects that are recurrent, but in a limited subject range. These are usually facets of concepts related to operations, techniques, processes, materials, agents etc. They are listed only in particular sections of the main tables. Special auxiliary numbers can be recognized as they all begin with one of these three specific symbols/indicators: .0 (point nought), - (hyphen) or ' (apostrophe). Any UDC number beginning with any of these symbols can be combined with any other UDC number in its designated area of application.

2. Common auxiliary tables

These tables contain common auxiliary signs and common auxiliary numbers.

2.1 Common 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.

+Coordination. Addition (plus sign). Table 1a
/Consecutive extension (oblique stroke sign). Table 1a
:Simple relation (colon sign). Table 1b
::Order-fixing (double colon sign). Table 1b
[]Subgrouping (square brackets). Table 1b
*Introduces non-UDC notation (asterisk). Table 1h
A/ZDirect alphabetical specification. Table 1h

2.2 Common Auxiliary Numbers

These are tables enumerating concepts that denote recurrent characteristics, applicable over a range of subjects; the auxiliary is simply added at the end of the number for the subject. 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.

=...Common auxiliaries of language. Table 1c
(0...)Common auxiliaries of form. Table 1d
(1/9)Common auxiliaries of place. Table 1e
(=...)Common auxiliaries of human ancestry, ethnic grouping and nationality. Table 1f
"..."Common auxiliaries of time. Table 1g helps to make minute division of time e.g.: "1993-1996"
-0...Common auxiliaries of general characteristics: Properties, Materials, Relations/Processes and Persons. Table 1k.
-02Common auxiliaries of properties. Table 1k
-03Common auxiliaries of materials. Table 1k
-04Common auxiliaries of relations, processes and operations. Table 1k
-05Common auxiliaries of persons and personal characteristics. Table 1k this table is repeated

UDC Synthetic Structure

UDC is an analytico-synthetic and/or faceted classification. It allows an unlimited combination of attributes of a subject and relationships between subjects to be expressed. UDC codes from different tables can be combined to present various aspects of document content and form, e.g. 94(410)"19"(075) History (main subject) of United Kingdom (place) in 20th century (time), a textbook (document form). Or: 37:2 Relationship between Education and Religion. Complex UDC expressions can be accurately parsed into constituent elements.


    Tourist maps of Grafton County (USA, Maine) from 1970s as a pdf file will be expressed as a combination of simple UDC numbers as follows:


    This expression is created from the following simple UDC numbers:

    338.48 Tourism
    (734.211.4) auxiliary number of place: Grafton County [USA, Maine]
    "197" time auxiliary number for 1970s
    (084.3) auxiliary number of form - map
    (0.034.2) auxiliary number of form - carrier - digital file