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 allows for detailed indexing of documents in all subjects (see subject coverage). This is achieved through two main features of UDC:
- detailed subdivision of hierarchies
- analytico-synthetic nature of the system, i.e. provision for synthesis of subjects, attributes and general characteristics across the universe of knowledge. The level of detail and specificity of UDC cannot be observed based on the hierarchy levels or from the number of UDC classes as most of compound and complex subjects are described through combination of simple UDC numbers in the process of indexing
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.