Customizing the metamodel : Using listof, oneof, and expressionof : ExpressionOf
  
ExpressionOf
ExpressionOf allows you to express references to objects using complex operators and delimiters. While System Architect expects you to use ExpressionOf to refer to data elements and data structures (DATA), it is not restricted to that use.
References defined with ExpressionOf are entered in a dialog box using the syntax
A + B + C
or
A +
B +
C
or
A
B
C
The elements may be written on one line or more than one line; the division between one element and the next is determined by white space. By convention, a + sign is used to divide the individual data items, but it is not required.
The following special operators and delimiters can be used in specifying expressions:
Symbol
Description
+
And (optional)
[...|...]
Either-or
{...}
Iterations of
i{...}j
Allow from “i” to “j” iterations of
(...)
The enclosed component is optional
@
The component is a key field
@n
The component is the nth element of the elements making up a compound key
*...*
The enclosed text is a comment
/.../
The enclosed text is a comment but has significance to the Schema Generator
Sub-expressions can be nested within other expressions. For example, ITERATIONS OF can be included within EITHER OR brackets.
[ n1{...}n2 | n3{...}n4 ]
Example of EXPRESSIONOF listbox