Syntax diagrams

A syntax diagram describes the context-free, abstract grammar of a product function.

A syntax diagram for example describes a language instruction, the structure of a configuration file, or the options of command-line tool.

The following rules are used in a syntax diagram:

Invariable syntax elements (keywords) are written in fixed font.
Language keywords are in uppercase, like INPUT BY NAME.
Variable syntax elements are written in italics.
Wildcard characters are used to indicate syntax elements that can either repeat, be mandatory or optional.

Table 1. Wildcard characters
Wildcard characters notation	Description	Example
`[ element ]`	Square brackets indicate an optional element in the syntax.	`IS [NOT] NULL`
`[ element-1 \| element-2 ... ]`	Square brackets with pipe separator indicate an optional element to be selected from the list.	`[ASC\|DESC]`
`{ element-1 \| element-2 ... }`	Curly brackets with pipe separator indicate a mandatory element to be selected from the list.	`{NONE\|X\|Y\|BOTH}`
`element` `[...]`	A sign made of square brackets with three dots indicate that the previous element can appear more than once.	`ident [...]`
`element` `[,...]` `element` `[:...]` `element` `[;...]` `element` `[\|...]`	A sign made of square brackets including a separator character (comma, colon, semi-colon, pipe) followed by three dots indicate that the previous element can appear more than once, and must be separated by the specified character.	`colname [,...]`

Example (dummy language instruction):

CREATE [ PRIVATE | PUBLIC ] SHAPE object-name
    WITH integer-expression { ROWS | COLUMNS }
    [ USING option [,...] ]

In this syntax diagram:

The CREATE keyword can be followed by PRIVATE or PUBLIC keywords, but these are not mandatory (square brackets are used)
object-name is a variable syntax element, to define the name of the object to be created.
integer-expression indicates an expression that must evaluate to an whole number.
The integer-expression must be followed by the mandatory ROWS or COLUMNS keyword (curly braces are used)
The whole USING clause is not required (square braces are used)
If the USING clause is specified, it must be followed by a comma-separated list of option elements.

For example, instructions using the above syntax could have the following forms:

CREATE SHAPE shape1
   WITH 5 ROWS

CREATE PRIVATE SHAPE shape2
   WITH 25 COLUMNS
   USING fragmentation, autoload