UDC, or Universal Decimal Classification, is a system for organizing and classifying library materials that was developed by Paul Otlet and Henri La Fontaine in the late 19th century. It is not based on any previous classification system, but rather represents a new approach to the organization of library materials.
The UDC system is based on the idea of organizing materials according to their subject matter using a system of decimal numbers. Each number represents a different category or subclass, and the relationships between the categories are indicated by the placement of the numbers. For example, a book about the history of agriculture might be classified using the notation “63:631,” which would indicate that it is a book about the history of agriculture, which is a subclass of “Agriculture,” which is a subclass of “Technology (applied sciences).”
The UDC system is widely recognized as a comprehensive and flexible system for organizing and classifying library materials, and it continues to be widely used in libraries around the world.