Dewey Decimal Classification

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The Dewey Decimal Classification system (abbreviated to DDC) is a method for classifying books and materials inside libraries designed by Melvil Dewey, an American librarian, and first published in 1876. It uses a floating decimal number to represent the subject of a book. There are 999 top-level categories (in principle, though some are not actually used) - the highest level of the taxonomy is represented by the first digit, then the second and third digits. After that, the numbers after the decimal point specify the subject as far as it needs to go. DDC was designed as a general classification system, attempting to cover all knowledge. This makes it applicable to many different types of libraries, ranging from school and public libraries, to research and special libraries, as well as libraries of different sizes. The current full edition of DDC is the 23rd edition.


The basic concept of DDC is that it is arranged by discipline, or field of study, in which all knowledge is divided into a number of broad areas. In DDC, the main division of knowledge is into ten main classes, based on discipline, not individual subject. These ten classes are then further subdivided to provide more detailed subjects and topics. The arrangement of these more detailed subjects and topics is hierarchical, beginning with the broader and dividing into the more specific.

Each discipline, subject and topic in DDC is represented by a specific notation, which, because of the underlying framework of division by ten, is a decimal system. The basic notation of DDC is three digits, but this can be extended for more specific topics by the inclusion of a decimal point and further numbers. DDC displays the details of the classification system in numerical order in the section referred to as the Schedules. The First Summary of DDC reflects the basic division of all knowledge into ten main classes. The specific class is represented by the first digit in the notation. DDC does not list every possible classification number in the Schedules. To do so would result in a large number of printed volumes. Instead, DDC allows more specific numbers to be built if certain circumstances occur.

DDC is available in print or online (WebDewey). WebDewey is updated as changes occur. DDC in print format is updated regularly every seven to ten years.


For instance, the 100 range covers philosophy, psychology and paranormalism. Within there, metaphysics is to be found at 110, ontology at 111 and paranormal phenomena is at 130. The Dewey system is widely used, but many find faults with it. Dewey artificially slices complex matters in order to fit everything into a decimal organisation. This can be reflected rather strangely on the shelf. The 100s are a perfect example, with academic philosophy books being mixed together with books on astrology and graphology. Similarly, in the 200 range, where religion is covered, Dewey is heavily oriented towards Christianity - as can be expected from someone in 19th century America - but it does cause categorisation to become interesting: Christianity and general religious topics are mixed together for categories 200-289, leaving 290 for "Other and comparative religions" - Judaism gets 296, while "Religions of Indic origin" gets 294. The whole system can often feel unbalanced.

While the Dewey system is widely used in many libraries at the local and school level, some academic, research and national libraries use different systems.[1] The Library of Congress uses its own system, as does the British Library in London. The libraries of the University of Oxford, University of Cambridge, University of London, University of Chicago, Duke University and many others are also using other systems, some based on the Library of Congress, others home-grown.