A transition can be activated by
an event caused by a button, and it can initiate an action. You may compare this to the
metamodel illustrated in Figure 9.9. The only difference is that the Event role nowhas
a Boolean property called ???Long press???? Its default value is false since a short press is
the more common case.
Once the metamodel is updated, we can next try out the language. Depending on
the tool (see the different alternatives in Chapter 14), you may need to generate the
metamodel for another tool or just use it immediately for modeling. Again, depending
on your tool you may need to de?¬?ne a new model or the tool can update the existing
models automatically for the changed language. Figure 10.8 describes a sample
model, in which the long press policy is used for the Down button. An ellipse and
related text are used in the notation to visually indicate the difference in the model.
Using both is perhaps overkill, but something is necessary to help read the model.
FIGURE 10.7 Metamodel having support for alternative button pressing policies
FORMALIZING LANGUAGES WITH METAMODELING 249
10.4 DEFINING LANGUAGE RULES
Along with modeling concepts, we also normally detect various domain rules,
constraints, and consistency needs which a language should follow. These rules
obviously need to be de?¬?ned too.
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