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. DDC numbers are listed in groups of three digits for ease of reading and copying. All entries (numbers, headings, and notes) should be read in the context of the hierarchy.
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.
Table numbers are given in full in the number column of the tables, and are never used alone.
There are six numbered tables in DDC 23:
T1 Standard Subdivisions
T2 Geographic Areas, Historical Periods, Biography
T3 Subdivisions for the Arts, for Individual Literatures, for Specific Literary Forms
T3A Subdivisions for Works by or about Individual Authors
T3B Subdivisions for Works by or about More than One Author
T3C Notation to Be Added Where Instructed in Table 3B, 700.4, 791.4, 808–809
T4 Subdivisions of Individual Languages and Language Families
T5 Ethnic and National Groups
Except for notation from Table 1 (which may be added to any number unless there is an instruction in the schedules or tables to the contrary), table notation may be added only as instructed in the schedules and tables
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. Bracketed numbers should never be used.
Standard subdivisions are also bracketed under a hook number, that is, a number that has no meaning in itself, but is used to introduce specific examples of a topic. Hook numbers have headings that begin with “Miscellaneous,” “Other,” or “Specific”; and do not contain add notes, including notes, or class-here notes. For example:
652.302 Specific levels of skill
[.302 01–.302 09] Standard subdivisions
Do not use; class in 652.3001–652.3009