04 The DDC hundred Divisions

Before we go on to list the thousand Dewey subject numbers and subject headings, let’s take a look at the broader structure. The DDC groups all subjects in TEN broad CLASSes, each starting with a round ‘hundreds’ number:

000      Generalities (Computer Science, Information, and General Works)

100      Philosophy and Psychology

200      Religion

300      Social Sciences

400      Language (and Linguistics)
500      Natural Sciences and Mathematics

600      Technology (Applied Sciences)

700      Arts (and Recreation)

800      Literature800 Literature

900      Geography and History (and Biography)

So these are the ‘Hundreds’. All the 900s – that means the numbers 900 to 999 - cover the field of Geography and History, and so on. Each of the Hundreds Classes is subdivided into ten DIVISIONS each (900 to 909, 910 to 919, and so on), each Division into ten SECTIONS. Ten Classes, into ten Divisions, into ten Sections each: totalling up to 10 X 10 X 10 = a 1000 Section numbers, a thousand subject heads.

I've put the hundred Divisions on their own Page...see the tabs at the top of the screen.

So where does the ‘Decimal’ in the DDC come in? That’s because the subdividing doesn’t stop here; the process goes right on, except that a decimal point is put after the 3-digit number. Thus 910 can be subdivided into ten sub-classes (910.0 to 910.9), each of these could be further divided into ten sub-sub-classes (910.90 to 910.99), and so on… to as many levels as we wanted. Strictly, the numbers ending in zero after the decimal point (like 910.0) are not given separate mention, so the total number of subdivisions may be 9, not 10 for each level. Each number is associated with an individual subclass of the main subject. This is usually set down in detail for each number, as each subject will be broken down in a domain-specific manner, but there are some broad conventions, such as .01 refers to the ‘philosophy’ or ‘theory’ of the main subject. There is in fact a Table of Standard Subdivisions, which we will describe later.

03 The Dewey Decimal scheme: playing by numbers

Now we can address the core problem, which is: how to arrange our non-fiction (the ‘subject-matter’) books in a meaningful manner. The basic premise is, of course, that we can identify one main subject of each book or report in our hands. Dewey has done half our job by listing out a thousand main subject names, starting not from 1, but 000, to 999, in a remarkably prescient manner which conforms neatly to the usual practice in our own computer age (all the numbers are 3-digit ones, hence can perfectly fitted into a fixed field in a database structure).

For the first round of classification, perhaps this is all that we will need to arrange our books subject-wise. Within each subject, naturally we will be arranging our books by the alphabetical ordering of author last-names, thus (Richard) Dawkins would come after (Charles) Darwin. If you had two books by Dawkins, you would arrange them by their date of (first) publication. These three fields: DDC three-digit code number, Author name, and Year, would suffice to order your books in a perfectly predictable sequence.

The whole structure depends on the expectation that any new subject could be ‘adjusted’ under these thousand heads. If you did have a subject that didn’t fit into a single one of them, of course you’d have a problem…then there would have to be a sufficient number of ‘empty’ numbers to cater to these eventualities. In practice, most subjects could be fitted as a sub-category under the thousand main categories provided by Dewey.

One great feature of this system is that if you walked into any library or looked up any catalogue that also followed the same classification scheme (the DDC in this case), you would expect to find your favourite books and authors in the same sequence. If you were interested in say Physics, you would zero in on the 500s; if in History and Geography, on the 900s. These are the Dewey 'hundreds', which bring together related subjects in groups. A little down the line, you will be glibly talking in numbers rather than in names. Unlike bookshops, where each manager devices an individual scheme of arranging the subjects, in academic and public libraries, all of them follow the same. This is spoilt to some extent by the fact that there are two or three main systems; fortunately, the second most common, the Universal Decimal Classification (UDC) closely follows the DDC, and the hundreds numbers are all quite similar.