Connie's Convenience Store - About Peter Coad

Selecting Problem-Domain Objects Connie’s Convenience Store 7
That’s four object-model components. There is a fifth one. It’s the “not this time”
component. It’s a bucket that holds objects that are interesting, ones that you consider,
yet that for one reason or another (be it technical, sociological, or economic), you’ve
decided not to include at this time. By using this component along with the others, you
can show what’s included—and what’s not.
By organizing classes this way, you facilitate simpler modeling this time (within
each model component).
You also increase the likelihood of reuse next time. Why? Here’s an example. Next
time, you might want to reuse certain problem domain classes, even though you may
choose to work with different human interaction classes.
What’s the alternative? Smash the model components together. But then the overall
model is harder to understand; and in the future, unless you choose the same problemdomain,
human-interaction, data-management, and system-interaction approach, reuse
is very unlikely. Ouch!
So, use model components. Use them as an overall outline, a guide for selecting objects.
And use them to keep your classes well-organized, for understanding, and for
reuse (Figure 1–3):
ProblemDomain HumanInteraction
SystemInteraction NotThisTime
Figure 1–3: Model components.
You can use these model components to organize your approach to building the
model.
In this chapter, you’ll go from PD to HI to DM to SI. In each case, you’ll use strategies
and patterns to help you:
– select objects
– establish responsibilities
– work out dynamics with scenarios.
SELECTING PROBLEM-DOMAIN OBJECTS
DataManagement
Take a walk on the wild side inside Connie’s Convenience Store. Look for objects, one
that the system might need to know or do something about.
Coming up, you’ll apply strategies for selecting objects:
– actors and participants
– places
– things.
For now, consider PD objects. (Later in this chapter, you’ll consider HI, DM, and SI
objects, too.)