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3.3.10 Signal
162 CHAPTER 3 UML??”Unifi ed Modeling Language
Classes that can receive signals describe this property similar to an operation,
but with the additional keyword ?«signal?» in front of the name ( Figure 3.21 ).
3.3.11 Data Types
Data types differ from classes in that their instances have no object identity. This
means that two instances with identical attribute values cannot be distinguished.
UML knows three forms of data types.
FIGURE 3-21
Example for send and receive signals.
class Send and receive signals
?«signal?»
Key
removed:Boolean
StartCarUsage
Key(removed:Boolean)
?«signal?»
Defi nitions
A data type is a type the instances of which can be identified solely by their
values.
A primitive type is a special data type that has no structures worth
mentioning.
An enumeration is a special data type the value range of which consists of a
limited set of defi ned literals.
Data types are used when we are interested only in a value but not in the object
identity. Examples for data types are period , date , current .


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