16.14. Constraints
Constraints may be used on most UML diagrams, but are especially common on class diagrams. A UML constraint is a restriction or condition on a UML element. It is visualized in text between braces; for example: { size >= 0 } . The text may be natural language or anything else, such as UML's formal specification language, the Object Constraint Language (OCL) [WK99]. See Figure 16.14.