Universal Decimal Classification (UDC) | UDC Claasification System

The Universal Decimal Classification (UDC) is a system of classification used for organizing and retrieving information in libraries, bibliographic databases, and other information systems. 

The UDC is based on the decimal system, which means that it uses a set of numbers to represent specific subjects and topics. 

The UDC was first developed in 1895 by the Belgian bibliographer Paul Otlet and is currently maintained by the UDC Consortium.

The UDC is a multilingual and multidisciplinary classification system that can be used for classifying information in any field or subject. It is designed to be flexible and adaptable, allowing for the creation of new classes and subclasses as needed.


The UDC is also hierarchical, with each level of classification becoming more specific than the previous one. The top level of the UDC consists of 10 main classes, which are:

0 Generalities

1 Philosophy. Psychology

2 Religion. Theology

3 Social sciences

4 Language. Linguistics. Literature

5 Natural sciences

6 Applied sciences. Medicine. Technology

7 The arts. Entertainment. Sports

8 Geography. Biography. History

9 Miscellaneous.

Each of these main classes is further divided into subclasses, which are represented by a two-digit number. For example, the subclass for mathematics is 51, and the subclass for chemistry is 54. The subclasses can then be further divided into more specific topics, which are represented by additional digits.

The UDC also includes a set of common auxiliary tables, which are used for indexing and retrieving information. These tables include:

Table 1: Common auxiliaries for geographic names

Table 2: Common auxiliaries for personal names

Table 3: Common auxiliaries for languages

Table 4: Common auxiliaries for time periods

Table 5: Common auxiliaries for legal systems and jurisdictions

Table 6: Common auxiliaries for forms of expression

Table 7: Common auxiliaries for materials

Overall, the UDC provides a comprehensive and flexible system for organizing and retrieving information in a wide range of fields and subjects.

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