| x=a | the data item x is defined by the specification a, where a is itself a data item to be defined or is a complete description of a set of attributes. |
| x=a + b | x consists of items a and b |
| x=[a|b] | x consists of a or b |
| x= (a) | the item is optional |
| x={a} | x consists of zero or more occurrences of a |
| x=y{a} | x consists of y or more occurrences of a |
| x={a}z | x consists of up to z instances of a (inclusive) |
| x=y{a}z | x consists of between y and z occurrences of a |