Connie's Convenience Store - About Peter Coad

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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.
Selecting Problem-Domain Objects Connie’s Convenience Store 9 Cashier, head cashier Cashier objects are a must; the system will assess each cashier’s performance. What about head cashier? What should you do here? One choice: you could model it as another kind of participant. In fact, you could model a head cashier as a special kind of, a specialization of, a cashier. When would you do this? Check out potential attributes. #68. “Partially Applicable Attribute” Strategy establishing responsibilities / what I know (consider and challenge) • Attribute that applies only to certain objects in a class? • Do you have an attribute which applies only to certain kinds of objects? • Do you have an attribute that may have the value “not applicable”? • If so, factor out the specialized attribute into a specialization class. Check out potential services. #121. “Partially Applicable Service” Strategy establishing responsibilities / what I do (consider and challenge) • Do you have a service that applies only to certain objects in a class? • Do you have a service that applies only to certain kinds of objects? • Do you have a service which tests for what kind it is, and then acts accordingly? • If so, factor out the specialized service into a specialization class. Add another participant class? Only if a head cashier object knows or does something different from what a cashier object knows or does. (Hmmm. No difference here.) Another choice: you could model it along with some other participant. Express simple variation with attribute values. In this case, you could treat a head cashier as a cashier with a greater level of authorization. The only difference is the value of its authorization level. This second choice makes sense here: at this point, just a difference in value seems to be enough.
Page 1 and 2: GETTING STARTED 1 Connie’s Conven
Page 3 and 4: Identifying System Purpose and Feat
Page 5 and 6: Selecting Objects Connie’s Conven
Page 7: Selecting Problem-Domain Objects Co
Page 11 and 12: Selecting Problem-Domain Objects Co
Page 19 and 20: Applying Patterns: Select and Organ
Page 29 and 30: Establishing Responsibilities for P
Page 55 and 56: Applying Patterns: Establish Proble
Page 57 and 58: Applying Patterns: Establish Proble
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Applying Patterns: Establish Proble
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Working Out Problem-Domain Dynamics
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Working Out Problem-Domain Dynamics
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Scenario: sale calculates its total
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Selecting Human-Interaction objects
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Establishing Human Interaction Resp
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Establishing Human Interaction Resp
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Working Out Human-Interaction Dynam
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Scenario: actual cashier logs on. S
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Scenario: sell item. Receipt SaleLi
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Scenario: get payment by check Rece
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Selecting System-Interaction Object
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Establishing System-Interaction Res
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Working Out System-Interaction Dyna
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Selecting Data-Management Objects a
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Working Out Data-Management Dynamic
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Progress at This Point Connie’s C
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Progress at This Point Connie’s C
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Wrap Up Connie’s Convenience Stor
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