When you define a model, you also define a number of constraints that has to be checked. For example, lower- and upper- bounds of a relationship's multiplicity, say (min=1, max=3), specify that an object cannot have less than one object (of a certain type!) in relation with itself, and no more than three as well. You can also mark an attribute as 'required' to avoid it being None.
The framework naturally verifies these constraints: the checking occurs automatically when an EditingContext is about to save changes (we will see hereafter how this can be manually triggered).
The constraints that are enforced are the following:
Comments are welcome: Sebastien Bigaret / Modeling Home Page