Requirement constraints

Constraints allow you to specify the requirement either informally using text statements (commonly known as "shall" statements) or more formally using constraint expressions.

A requirement constraint is built from two sets of other constraints: the assumed and required constraints of the requirement. 

• A require constraint states the required constraints imposed on the model, expressed formally or informally in the requirement.
• An assume constraint states the assumed constraints imposed on the model, expressed formally or informally in the requirement.

Required and assumed constraints are declared as composite constraint usages in the body of a requirement definition or usage. The required constraints of a requirement only apply if all the assumed constraints are satisfied. A requirement is satisfied for a subject only when both constraints are true.