Diagrams - General Diagram Features - Constraints

4 important questions on Diagrams - General Diagram Features - Constraints

What is a constraint?

A constraint is a rule that prohibits some potential values for a field

Where is a common way to place the constraint?

In UML, constraints can be added to many places on a diagram.

One common way is to place the constraint inside a comment symbol.

How can we identify that it is a constraint?

To identify it is a constraint the text of the constraint is surrounded by curly braces, {}.

The BNF for a constraint is as follows:

<constraint> ::= ‘{’ [ <name> ‘:’ ] <boolean-expression> ‘}’ where <name> is the optional name of the Constraint.

If the <name> field appears it is followed by the colon ‘:’.

<boolean-expression> is the textual form for the Constraint.

It is required to have either a true of false value when evaluated.

The whole expression is surrounded by curly braces ‘{}’.

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