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2.4 Modeling Use Cases
FIGURE 2-56
Standard fl ow for ??? start car usage. ???
act Start car usage
Car usage started
?«essential?»
Identify
customer
?«essential?»
Check usage
right
?«essential?»
Unlock car
?«essential?»
Start car
usage
?«essential?»
Check disposal
right
?«essential?»
Activate car
?«essential?»
Confirm usage
start
92 CHAPTER 2 The Pragmatic SYSMOD Approach
These conditions have to mutually exclude each other to ensure that no more
than one condition is met ever. Of course, we also have to ensure that one single
condition is always met. If there are several conditions, i.e., no pure yes/no decisions,
it is useful to add the keyword [ else ] to a fl ow, which will then be activated
whenever all other conditions are wrong. This allows us to achieve a complete
coverage of all possibilities.
Similarly to fork and join nodes, there is a counterpart to decision nodes.
A merge node looks like a decision, except that it has several incoming fl ows and
only one outgoing fl ow. No decisions are denoted.


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