Connie's Convenience Store - About Peter Coad

8 Connie’s Convenience Store Selecting Problem-Domain Objects
Select actors and participants
An actor is a person, an organization, or some other thing that participates in one or
more ways over time. A participant participates in a specific way, plays a role, fulfills a
specific mission.
What are the actors and participants in this system?
#13. “Select Actors” Strategy selecting objects (pattern players)
• Look for actors: people and organizations that act as participants within the system under
consideration.
• Examples: person, organization (agency, company, corporation, foundation).
Here, the actor is:
– person.
Organization could be interesting, too. Maybe later.
#14. “Select Participants” Strategy selecting objects (pattern players)
• Analyze how each actor participates, in ways that might be of interest to the system under
consideration.
• Why. Each actor participates in one or more ways through time. It’s the same actor, just
different ways of participating.People talk about wearing “different hats” during the day.
That’s exactly what such participation is all about.
• Examples: agent, applicant, buyer, cashier, clerk, client, civilian, customer, dealer,
delegate, distributor, donor, employee, investor, manufacturer, member, officer, official,
order clerk, owner, participant, policy holder, professional, prospect, recipient, retailer,
sales clerk, sales rep, shipper, student, subscriber, supervisor, supplier, suspect, teacher,
wholesaler, worker.
In what interesting ways does a person participate when using a point-of-sale system?
Why, there’s:
– cashier
– head cashier
– customer.
What objects do you need? The system purpose and features give you a standard, a
checkpoint, for making that decision. Here’s how. If an object fits within the context of
the system’s responsibilities, then include it. If not, then (1) add to the system features
or (2) put that object in the “not this time” model component.
Consider cashier, head cashier, and customer.