However, making reuse of
models explicit generally makes it easier to maintain them and concretely shows
the dependencies of the various components. For instance, a change in the Alarm
application to require an extra button would affect which physical designs of
watch the Alarm could be used in. If Alarm had simply been reused, this effect
might not have been obvious. If, however, there were a top-level model showing
each member of the watch product family, which physical watch body it used, and
which watch applications it contained, the effects of that change would be easier
to see.
If there was a need for a mapping between the buttons mentioned in a watch
application model and those present in a physical watch, there was also the question of
how to model this mapping. Would the mapping be included as part of the top-level
family model, or would it be a separate kind of model between the top-level family
model and the actual watch applications? Further, who would be responsible for
building these mappings: the watch application designer, the family designer, the
designer of a particular watch model, or somebody else? Similarly, would a separate
mapping be required for each pair of a watch application model, for example a
stopwatch, with a physical watch body, or could one mapping be reused over many
watch applications or physical watch bodies?
The question of the mapping was thus dif?¬?cult in both technical and organizational
terms, and also hard to decide at this early stage.
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