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However, its most common use is in interaction diagrams.
In Figure 3.81 , the time when the customer card is placed on the card reader
(@ t ) and the time when the car doors are unlocked (@ s ) are measured. @ speci-
fi es the action at the measurement of time. The measured values are put into the
3.8 Interaction Diagrams
FIGURE 3-81
Example for time constraints.
sd Unlock car
:Customer
:On-board
computer
Reservation system Car central locking
system
Card &sms1
Check usage right
&sms2
Usage right
Unlock car
@t
@s
{t-s < 2}
t:Time
s:Time
sms1:Duration
sms2:Duration
FIGURE 3-80
Example for a state invariant.
sd Driving a car [incl. filling tank]
:Tank
ref
Full
Full
Empty
ref Fill tank
Driving a car
:Engine
Engine is off
Engine is off
214 CHAPTER 3 UML??”Unifi ed Modeling Language
time constraint and describe that the entire process may not take longer than 2
minutes ({ t  s  2}). The on-board computer and the reservation system communicate
via SMS. The duration of the transmission is measured ( & sms1 , & sms2 ).


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