OCUP2F 03 OCL

Module 3. Object Constraint Language⌘

References⌘

• OCL Specification Document (Version 2.0 or 2.2; Chapter 7 – All) http://www.omg.org/spec/OCL/

Object Constraint Language (OCL)⌘

• OMG Specification
• Object Constraint Language (OCL), a formal language used to describe expressions on UML models

Why OCL?⌘

• A UML diagram is typically not refined enough to provide all the relevant aspects of a specification.
• There is a need to describe additional constraints about the objects in the model.
• Such constraints are often described in natural language. Practice has shown that this will always result in ambiguities.
• OCL is a formal language that has been developed to fill this gap.
• OCL expressions do not have side effects (i.e., their evaluation cannot alter the state of the corresponding system).

Class Diagram Example⌘

Context⌘

Context of an OCL expression within a UML model can be specified through:

• context declaration:

context Company
  self.numberOfEmployees > 50

• in a diagram, with dashed lines to connect it to its contextual element

Invariants⌘

• Invariant is OCL expression that must be true for all instances of a classifier at any time.

context Company inv:
  self.numberOfEmployees > 50

Pre- and Postconditions⌘

context Typename::operationName(param1 : Type1, ... ): ReturnType
  pre : param1 > ...
  post: result = ...

context Company inv:
  self.numberOfEmployees > 50

Invariants⌘

context Company inv:
  self.numberOfEmployees > 50

context Company inv enoughEmployees:
  self.numberOfEmployees > 50

Invariants⌘

context Company inv:
  self.numberOfEmployees > 50

Invariants⌘

context Company inv:
  self.numberOfEmployees > 50

Basic OCL types⌘