Connie's Convenience Store - About Peter Coad

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16 Connie’s Convenience Store Selecting Problem-Domain Objects Sale One of the transactions is sale. Check it out. (Peter) Connie, what are the main things you do with a customer? (Connie) We sell items. (Peter) Do you have a special name for that? (Connie) A special name? “Sale.” (Now isn’t that special.) (Peter) Does it include only items you sell to a customer? (Connie) Now that you mention it, a sale may include both sales and returns. Hold it! The domain vocabulary is “sale.” Someone on our team might argue that you should use a more accurate term, “sales transaction.” Advice? Don’t do it. Key point: don’t ever change domain vocabulary unless your customer sees the need for and wants to make the change (otherwise you’ll be forever mapping her words to your words; that’s both counterproductive and a real nuisance). Most transactions have parts, called transaction line items. A sale is no exception. A sale is a collection of some number of sale line items. Add the classes: sale and sale line item (Fig. 1-8). Kinds of sales #34. “Select Kinds of Objects” Strategy selecting objects (kinds of objects) • Use generalization-specialization (gen-spec) to find additional classes. Look at each class as a generalization. Name its specializations, ones that fit with system objectives. Look at each specialization. Name its generalizations, ones that fit within system objectives. • Use gen-spec for domain-based reuse within an application; use configuration management for reuse across multiple applications, even multiple problem domains. • Use gen-spec to show domain-based “what’s the same, what’s different,” within an application. • Examples: equipment, kinds of equipment; participants, kinds of participants; transactions, kinds of transactions. Consider the kinds of sales: – sales, returns. Do you need to distinguish between a sale and a return? (Peter) What’s the difference between a sale and a return? (Connie) The only difference is whether the amount is positive or negative. You don’t need to add classes for both “sale” and “return.” At this point, the system’s responsibilities for them appear to be identical. The only difference is whether the amount is positive or negative.
Selecting Problem-Domain Objects Connie’s Convenience Store 17 Payment Payments are important, too. No kidding! (Peter) What kinds of payments do you accept? (Connie) Cash, check, charge, or a combination of those. (Peter) Really, a combination? (Connie) Yes, especially in the wee hours of the morning. You’d be surprised. (Peter) I’ll take your word for it. Cash, check, and charge are kinds of payments. Do you need to know and do different things, based upon the kind (or kinds) of payment? Probably so. So add these specialized classes to your object model. As you go along, you might end up sliding them over into the “not this time” bucket. And that’s okay. You’re learning more and more about what’s really needed for this system under consideration. Here’s how to model gen-spec (Figure 1–7): Payment Cash Check Charge Figure 1–7: Gen-spec. The gen-spec icon is a semicircle. Generalizations connect to the rounded edge; specializations connect to the straight edge. By convention, a generalization class may or may not have objects; lowest-level specialization classes must have directly corresponding objects. Here, the generalization class does not have directly corresponding objects. Session Sessions? Are they important? Yes. Based upon the system features, you need to assess cashier performance. To make that calculation, you will probably want to know all of the corresponding sessions for that cashier. Adding transactions to your object model Add the following classes to your object model: – sale, sale line item – payment, check, cash, charge – session. See Figure 1–8:
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 and 8: Selecting Problem-Domain Objects Co
Page 15: 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 61 and 62: Working Out Problem-Domain Dynamics
Page 63 and 64: Working Out Problem-Domain Dynamics
Page 65 and 66: 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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Connie's Convenience Store - About Peter Coad

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