"The Universal Decimal Classification (UDC) is the world's foremost multilingual classification scheme for all fields of knowledge, a sophisticated indexing and retrieval tool. It was adapted by Paul Otlet and Nobel Prizewinner Henri La Fontaine from the Decimal Classification of Melvil Dewey, and first published (in French) between 1904 and 1907. Since then, it has been extensively revised and developed, and has become a highly flexible and effective system for organizing bibliographic records for all kinds of information in any medium (it is well suited to multi-media information collections). It is structured in such a way that new developments and new fields of knowledge can be readily incorporated. The code itself is independent of any particular language or script (consisting of arabic numerals and common punctuation marks), and the accompanying class descriptions have appeared in many translated versions. UDC is in worldwide use, and has been published in whole or in part in 40 different languages. The Multilingual Universal Decimal Classification Summary - UDC Summary (udcS) for short - represents a selection of around 2,600 classes extracted from the UDC Master Reference File (UDC MRF) 2011 which contains over 70,000 classes. The selection comprises main numbers, common auxiliary numbers and special auxiliary numbers and it represents even coverage of all areas of knowledge as contained by the scheme. UDC is updated annually and UDC Summary represents always the latest version of UDC. The UDC Summary is held in a multilingual database that mirrors the structure of the UDC MRF database and in that respect represents the full set of data and can be used as a UDC demonstrator for training, research, various information organization and retrieval purposes."