106 CHAPTER 2 The Pragmatic SYSMOD Approach
It means that a block has more than one generalization relationship with other
blocks. Nevertheless, you should use multiple inheritance very sparingly.
Pay attention to circles in your domain knowledge model ( Figure 2.69 ). They
are not illegal, but they indicate that there is likely to be redundant information.
In such a case you should check each association from the circle outward as to
its importance. Try to do this by imagining you removed an association from the
diagram and are trying to see whether or not your model lost some of its expressiveness.
If you fi nd an unimportant association, remove it.
Make sure your domain knowledge model doesn ??™ t turn into a design model. The
primary goal is to describe the domain structures. Particularly software developers
who are familiar with design patterns and various design tricks relating to class
modeling have to be aware of this delimitation.
FIGURE 2-68
A generalization in the domain knowledge model.
bdd [package] Domain knowledge [generalization]
Route Route
type: RouteKind
Quick route Short route Simple route
?«enumeration?»
RouteKind
short
simple
quick
FIGURE 2-69
Circles in the domain knowledge model.
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