Indexing and Retrieval with UDC

The UDC was the first classification scheme to be used for information retrieval in an online environment. The applications range from enriching simple KWIC indexes to OPACs.

It is easy to search on each of the separate elements of a compound or complex notation or on those numbers in combination. It also possible to search on words in combination with numbers post-coordinately, but this depends entirely on the quality of the system itself and the way classification data are stored in the database.

The UDC can be used in a concordance with a subject heading system, thesaurus or other form of partially-controlled vocabulary, where class numbers can serve as place-holder for verbal expressions in one or more languages.

The synthetic structure of the UDC is a major advantage in a retrieval system in comparison with enumerative or semi-enumerative classification like the Library of Congress Classification or the Dewey Decimal Classification. In the UDC system, it is possible to combine any two numbers from the schedules. This enables the building up of compound and complex notations to express concepts, which are not explicitly specified in the schedules.

The individual elements, which constitute a compound UDC number, are clearly marked by symbols and punctuation (or facet indicators). Additionally, a different symbol or facet indicator introduces each concept. This is a major advantage for information retrieval because each concept in the compound structure can be searched separately.

For example, instead of using an established, pre-coordinated arrangement, the separate elements may be rearranged (post-coordinated) and searched by using Boolean logic operators.

	“16” AND (71) everything on Canada in 17th century
	“16” OR (71) either those on Canada, or those on 17th century
	“16” NOT (71) 17th century but excluding those among them relating to Canada