Introduction

The DDC is a born enumerative knowledge organization system. That is, class numbers for most known subjects are given ready-made. Sometimes known as a ‘mark and park’ system, it allows a classifier to pick the right number from the schedules and mark it on the document, typically for shelf placement. Over the years the DDC has made many provisions for number synthesis1 for in-depth subject analysis, to cope with the complexity and quantitative growth of knowledge. Now, number-building provisions are so extensive that the system can accommodate many more numbers than are explicitly listed in the schedules.

Identifying the best number for a resource often requires building onto a base number. This means extending a number in the schedules, using all or part of another number taken, from the schedules or tables, to make a more specific number, i.e. to represent the subject more closely. Though class numbers for many topics are still found ready-made in the DDC, over the years the frequency of and facilities for number building have steadily increased. Specific number-building instructions are found in notes beginning with ‘Add to’. Number building should only follow such explicit instructions, with the major exception of addition from Table 1 Standard subdivisions, which can be added anywhere unless instructed otherwise. The number to be added to a given base can come from as wide a range as 001–999 to as narrow as say, 381.41–381.45.

The process of synthesis can be broadly categorized as follows:

• • adding to a given base any full number from the schedules

• • adding a part of a number to a given base taken from a whole main class

• • adding a part of a number taken from the same division or section

• • adding from an internal table

• • adding through a facet indicator

• • adding from any of the six tables.

These categories are, however, superficial, as the building process in all cases is the same. The technique of synthesis poses no problem provided one selects the right base number and follows the add instructions therein.

Note that adding numbers in the context of the DDC never means arithmetic addition. Rather, it means suffixing the full or specified slice of a number to the right of the specified base number.