Connie's Convenience Store - About Peter Coad

Establishing Responsibilities for Problem-Domain Objects Connie’s Convenience Store 31
What does a person object do?
The same basics that every object does:
– get . . . an attribute value
– set . . . an attribute value
– add . . . a connection to another object
– remove . . . a connection to another object
– delete . . . that object.
What does the person class itself do? The same basics that every class does:
– create (and initialize) . . . a new object.
You don’t need these basic services in your object model. You will find occasional
use for them within a scenario view.
What if you did put them everywhere? You’d have to add a half dozen labels to
every class with objects. Ugh! That’s a lot of added model complexity, with little gain in
model effectiveness. You see, notation is not free; every piece must pay its way, improving
understanding enough to warrant the added complexity. As one person so eloquently
put it:
“The ability to simplify means to eliminate the unnecessary
so that the necessary may speak.”
—Hans Hoffman
What about for person and participant?
#94. “Establish Actor and Participant establishing responsibilities /
Services” Strategy what I do (pattern players)
• For an actor or participant, include: calculate for me, rate me, is .
• For an actor as a collection, include: how many, how much, rank participants, calculate
over participants (plus services to enforce business rules across that collection).
• For a participant as a collection, include: how many, how much, rank transactions,
calculate over transactions (plus services to enforce business rules across that
collection).
Usually, the more interesting “what I do” behavior is done by the participant objects.