OCL
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Introduction
- How can we express constraints in UML ?
- E.g. the balance attribute in a SavingsAccount class can never be less than zero and more than 100000.
- UML only has a notion of an informal constraint in terms of a note - which can be attached to a model. However its just text.
- To write formal and machine checkable constraints - we use the Object Constraint Language (OCL).
Assertions
- In a program, assertions express constraints on program state that must be true at a specified point during execution.
- In a model/diagram, they document what must be true of an implementation of a modelling element.
