How to read syntax diagrams

The following rules apply to the syntax diagrams that are used in this information:

  • Read the syntax diagrams from left to right, from top to bottom, following the path of the line. The following conventions are used:
    • The >>--- symbol indicates the beginning of a syntax diagram.
    • The ---> symbol indicates that the syntax diagram is continued on the next line.
    • The >--- symbol indicates that a syntax diagram is continued from the previous line.
    • The --->< symbol indicates the end of a syntax diagram.
  • Required items appear on the horizontal line (the main path).
    Read syntax diagramSkip visual syntax diagram required_item
  • Optional items appear below the main path.
    Read syntax diagramSkip visual syntax diagram required_item optional_item

    If an optional item appears above the main path, that item has no effect on the execution of the syntax element and is used only for readability.

    Read syntax diagramSkip visual syntax diagram required_item optional_item
  • If you can choose from two or more items, they appear vertically, in a stack.

    If you must choose one of the items, one item of the stack appears on the main path.

    Read syntax diagramSkip visual syntax diagram required_item required_choice1required_choice2

    If choosing one of the items is optional, the entire stack appears below the main path.

    Read syntax diagramSkip visual syntax diagram required_item optional_choice1optional_choice2

    If one of the items is the default, it appears above the main path, and the remaining choices are shown below.

    Read syntax diagramSkip visual syntax diagram required_item default_choiceoptional_choiceoptional_choice
  • An arrow returning to the left, above the main line, indicates an item that can be repeated.
    Read syntax diagramSkip visual syntax diagram required_item repeatable_item

    If the repeat arrow contains a comma, you must separate repeated items with a comma.

    Read syntax diagramSkip visual syntax diagram required_item ,repeatable_item

    A repeat arrow above a stack indicates that you can repeat the items in the stack.

  • Sometimes a diagram must be split into fragments. The syntax fragment is shown separately from the main syntax diagram, but the contents of the fragment should be read as if they are on the main path of the diagram.
    Read syntax diagramSkip visual syntax diagram required_item fragment-name
    fragment-name
    Read syntax diagramSkip visual syntax diagram required_item optional_item
  • A b symbol indicates one blank position.
  • Keywords, and their minimum abbreviations if applicable, appear in uppercase. They must be spelled exactly as shown. Variables appear in all lowercase italic letters (for example, column-name). They represent user-supplied names or values.
  • Separate keywords and parameters by at least one space if no intervening punctuation is shown in the diagram.
  • Enter punctuation marks, parentheses, arithmetic operators, and other symbols exactly as shown in the diagram.
  • Footnotes are shown by a number in parentheses; for example, (1).