Universal Decimal Classification (UDC) Explained

The Universal Decimal Classification (UDC) scheme is a widely used system for organizing information and documents in libraries, archives, and other information centers worldwide. It is an intricate system that builds upon the foundational principles of the Decimal Classification (DC) developed by Melvil Dewey.

Understanding Classification Schemes

To understand what type of classification UDC represents, it's essential to define the primary types of classification schemes:

• Enumerative Classification: In an enumerative classification scheme, all possible subjects and their subdivisions are listed or "enumerated" beforehand. The classifier simply selects the pre-defined number for the specific subject of the document. These schemes are often less flexible in accommodating new or complex subjects because they require a complete listing of all possible topics. An example is the original Dewey Decimal Classification (DDC), which, in its earliest forms, was predominantly enumerative.
• Faceted Classification: A faceted classification scheme breaks down subjects into their constituent "facets" or fundamental categories (e.g., personality, matter, energy, space, time for a book). Each facet has its own set of terms and notation. Classifiers combine notations from different facets to build a precise classification number for a specific document. This approach offers great flexibility, specificity, and hospitality to new subjects because it allows for the synthesis of new subject numbers from existing components rather than requiring enumeration of every possible combination. Ranganathan's Colon Classification is a prime example of a purely faceted scheme.

Universal Decimal Classification: A Hybrid Approach

The Universal Decimal Classification (UDC) is not purely enumerative, nor is it rigidly faceted like the Colon Classification. Instead, it exhibits characteristics of both, leaning significantly towards a faceted approach while retaining an enumerative base. This is why it is often described as an "Almost - Faceted classification."

• Enumerative Base: UDC starts with a hierarchical structure, similar to DDC, where subjects are listed and arranged from general to specific using decimal notation. This initial enumeration provides a foundational framework.
• Faceted Features: UDC significantly enhances its flexibility through the extensive use of auxiliary tables (common and special auxiliaries). These tables represent various "facets" such as:
  • Common Auxiliaries: These can be applied across many subjects. Examples include notations for language $(=...)$, form $(\text{.0...})$, place $(\text{(1/9)})$, time $(\text{"..."})$, and points of view $(\text{.00...})$.
  • Special Auxiliaries: These are specific to certain main classes or divisions and allow for more detailed specification within those subjects.
  By combining notations from the main tables and various auxiliary tables, classifiers can construct highly specific and compound subject numbers. For instance, a book on "The history of French art in the 20th century" can be classified by combining notations for art, France, history, and the 20th century, even if that specific combination wasn't explicitly enumerated.

This ability to synthesize complex subject notations from simpler components, facilitated by the auxiliary tables and synthesis rules, is the hallmark of a faceted classification. However, because it still relies on a hierarchical, enumerative backbone before applying these faceted features, it is accurately characterized as "Almost - Faceted classification" or sometimes a "semi-faceted" or "analytico-synthetic" scheme.