Notational Hierarchy

Through the use of a 10-based decimal style of creating numbers, he allowed for each of these ten main classes to be further divided into ten sections, which can further divide into ten, and so on. These divisions are reflected in the various digits of the numbers created from DDC schedules. For example, 300 is the main class for Social Sciences, 320 is the division for Political science, and 324 is the section on The Political Process. Through adding a digit (i.e. replacing the ‘0’) from left to right, the number created gets more specific within a given subject. This concept is known as Notational Hierarchy, meaning that numbers are created in DDC through the process of breaking large areas of knowledge into more specific divisions. Here is another example of this process:

600 Technology

630 Agriculture and related technologies

636 Animal husbandry

636.7 Dogs

636.8 Cats

                                                                            <DDC 13th abridged ed., p. xxvi

In the above example, the main class is Technology (indicated by a 6). This is further divided into Agriculture (indicated by a 3 added to the 6). Further specification is made through dividing Agriculture into sections (here Animal husbandry, indicated by a 6), and Animal husbandry is divided into specific types of animals (here a 7 or an 8 added to indicate Dogs or Cats). This type of hierarchy is found all through DDC.

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