Dewey Decimal Classification
The Dewey Decimal Classification (DDC, also called the Dewey Decimal System) is a proprietary system of library classification developed by Melvil Dewey in 1876, and has been greatly modified and expanded through 22 major revisions, the most recent in 2004. This system organizes books on library shelves in a specific and repeatable order that makes it easy to find any book and return it to its proper place.
A designation such as Dewey 16 refers to the 16th edition of the DDC
The DDC attempts to organize all knowledge into ten main classes. The ten main classes are each further subdivided into ten divisions, and each division into ten sections, giving ten main classes, 100 divisions and 1000 sections. DDC's advantage in using decimals for its categories allows it to be both purely numerical and infinitely hierarchical. It also uses some aspects of a faceted classification scheme, combining elements from different parts of the structure to construct a number representing the subject content (often combining two subject elements with linking numbers and geographical and temporal elements) and form of an item rather than drawing upon a list containing each class and its meaning
Library of Congress Classification
The Library of Congress Classification (LCC) is a system of library classification developed by the Library of Congress. It is used by most research and academic libraries in the U.S. and several other countries. It is not to be confused with the Library of Congress Subject Headings or Library of Congress Control Number.
The classification was originally developed by Herbert Putnam in 1897, just before he assumed the librarianship of Congress. With advice from Charles Ammi Cutter, it was influenced by Cutter Expansive Classification, and the DDC, and was specially designed for the special purposes of the Library of Congress. The new system replaced a fixed location system developed by Thomas Jefferson. By the time of Putnam's departure from his post in 1939, all the classes except K (Law) and parts of B (Philosophy and Religion) were well developed. It has been criticized as lacking a sound theoretical basis; many of the classification decisions were driven by the particular practical needs of that library, rather than epistemological considerations.
Although it divides subjects into broad categories, it is essentially enumerative in nature. It provides a guide to the books actually in the library, not a classification of the world
The National Library of Medicine classification system (NLM) uses the classification scheme's unused letters W and QS–QZ. Some libraries use NLM in conjunction with LCC, eschewing LCC's R (Medicine). Others prefer to use the LCC scheme's QP-QR schedules and include Medicine R
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