Dynamic Constraints

Rules that describe how business concepts and their relationships are affected by  the operations of components.

Types of dynamic constraints

• Invariants

  •  A logical statement associated with an interface that a component assumes is always true.

  •  Ensure that component implementation will not invalidate the invariants defined by the interface.

  •  OCL representation for invariant: “inv logical statement”

• Preconditions

  •  A logical statement associated with a method in an interface that must be true before that method can be invoked.

  •  Client code should make sure that the precondition is true before it invokes the method.

  •  Incase, the client fails to make such a check, the component should gracefully exit using Exceptions.

  •  OCL representation for precondition: “pre logical statement”

• Postconditions

  •  A logical statement associated with a method in an interface that must be true after that method is invoked.

  • Component is responsible for ensuring postconditions of its interface methods.

  • Postcondition can refer to the component state or any of the method parameters.

    • To refer to previous value of the component state or method parameter, it uses @pre modifier.

  • OCL representation for postcondition: “post logical statement”