This change was put in the language as a modeling concept and no further actions were
needed: new applications could then use separate processes. If an existing model
wants to use the functionality provided by the new concept, it can be done naturally
with a small change to the model.
If the added concept changes rules and makes some existing models illegal, you
must decide how to change the models, if at all. Often no model update is needed here
since the models are still usable: the generator still produces working code with the old
models. If you prefer that models are updated to follow the new constraint, the most
typical decision is to inform modelers on those parts in the models that have become
invalid. They can then see the model context and decide on actions for their update. If
the added rule is well bounded and the model update policy is easy to formulate, you
can use tools to de?¬?ne the model update transformation.
10.8.2 Removing Modeling Concepts
Removing and modifying existing concepts needs to be done more carefully: most
likely these changes will have an effect on existingmodels.Goodmodeling tools should
allow using existing models even if some elements of the metamodel are removed.
When the language is modi?¬?ed, the easy way out is to freeze the current language
and continue its use only for application maintenance purposes.
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