Entries
Entries in the schedules and tables are composed of a DDC number in the number column (the column at the left margin), a heading describing the class that the number represents, and often one or more notes. All entries (numbers, headings, and notes) should be read in the context of the hierarchy.
In the print version of the DDC, the first three digits of schedule numbers (main classes, divisions, sections) appear only once in the number column, when first used. They are repeated at the top of each page where their subdivisions continue. Subordinate numbers appear in the number column, beginning with a decimal point, with the initial three digits understood.
Some numbers in the schedules and tables are enclosed in parentheses or square brackets. Numbers and notes in parentheses provide options to standard practice. Numbers in square brackets represent topics that have been relocated or discontinued, or are unassigned. Square brackets are also used for standard subdivision concepts that are represented in another location. Numbers in square brackets are never used.
Number Building
Only a fraction of potential DDC numbers are included in the schedules. It is often necessary to build or synthesize a number that is not specifically listed in the schedules. Such built numbers allow for greater depth of content analysis. There are four sources of notation for building numbers: (A) Table 1 Standard
Subdivisions; (B) Tables 2–6; (C) other parts of the schedules; and (D) add tables in the schedules.
Number building is initiated only upon instructions in the schedules (except for the addition of standard subdivisions, which may take place anywhere unless there is an instruction to the contrary). Number building begins with a base number (always stated in the instruction note) to which another number is added.