The structure of a class is defined by the sum of its attributes. Here the abstraction
of the model compared to the real world plays an important role. The attributes
reflect only the structure that is relevant for the model. For example, the class
customer in Figure 3.9 has no attribute for the color of the customer ??™ s eyes, but it
does have one for the name or the PIN check code. In another system the color of
the eyes might indeed be a relevant attribute.
The type of an attribute is denoted behind the attribute ??™ s name, separated by a
colon. Objects created on the basis of the class ??™ building plan include one value of
attribute type for each of that class ??™ attributes. This type is often itself a class??”the
building plan of the attribute.
An attribute can also be defi ned such that it contains several values of the
same type. The so-called multiplicity is denoted within square brackets behind
the type. It describes an interval ( Table 3.1 ) that defi nes the possible number. For
example, a customer object can contain any number of route objects in the range
0??“5 ( Figure 3.
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