40 ).
Similar to activity parameters, pins can also have the stream property. This
means that new data can be accepted over input pins, or previously created data
can be passed on over output pins while the action is still active. Pins with this
property are denoted with the keyword {stream} ( Figure 3.41 ).
So-called control pins play a special role. A control pin is not a model element
in itself, but a property of a pin ( isControlType ). An input pin with this property
accepts object tokens, but it doesn ??™ t pass the object (i.e., the data) to the action.
In this case, the object token has the same effect as a control token, except that
control tokens cannot be buffered. SysML utilizes this property for the control
operator and the control value.
Pins with this property are often not represented in the diagram. If they are,
then they are denoted with {control} next to the pin name.
There are approximately 40 predefi ned actions in UML. This set includes
actions that read and write values, actions that compare, create, and destroy
objects, and actions that invoke a behavior or an operation.
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