FIGURE 2-19
Searching for a matching actor.
Customer card
Card reader
Customer
53
But let ??™ s go back to our selection of actors in Figure 2.19 . We decided to use
customer which means, e.g., that card reader and keyboard are part of the system.
In terms of systems engineering, we take a holistic view of the system. This
allows us to then derive requirements for the card reader, which is to be purchased
from a third party, or evaluate other conceivable access systems, such as a
cell phone (see Section 2.8.1). Altogether, we now have the system context model
fully worked out, as shown in Figure 2.21 .
When searching for actors we normally run into elements that are not outside
but inside our system. Now, what do we do with this information? We cannot
model these elements as actors, since actors are outside the system by defi nition.
Of course, we won ??™ t discard this information for the only reason that it is not
needed in this work step; instead, we add it. Model an element found as a so-called
block and use the composite relationship to connect it with the entire system
( Figure 2.
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