application configuration
Now that we are done with an iteration of domain modeling, let’s see how we can configure a particular application for a specific set of requirements.
At the bottom of the page, we can see the complete model which combines final models from Parts I and II.
As the first step, we need to choose a jurisdiction, let’s say Canada except Quebec.
By constraints propagation, this configures
advancedOrExtendedLeft and behind features for
us.
Since we’re outside of Quebec, which requires
horizontal, we still have a choice of
orientation. Let’s choose vertical for our
application.
Next, we learn that in Canada redAndYellowToGreen and
allWayFlashingRedAsStop are not used but
allWayYellow is used. We could explicitly assert that but
since it’s a piece of knowledge we elicited during this application
engineering, let’s contribute it back and add a constraint back to our
domain model.
Now, we move on to the particular requirements of our application.
We now have to make a choice for the type of
advancedOrExtendedLeft we want: leftArrow.
Note that in a given jurisdiction, both options may be allowed; however,
for a single application, at most one is allowed, which is why we must
explicitly eliminate greenFlashing.
Let’s say that the dedicated right green arrow is not needed, so we eliminate it to reduce the cost.
The last choice is the countdownTimer, which we don’t
need.
Let’s check the allowed states of our system in our application:
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We have now properly configured a single traffic light. Let’s focus
on an application scenario with two traffic lights in opposite
directions: 
two traffic
lights
