Connie's Convenience Store - About Peter Coad

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40 Connie’s Convenience Store Establishing Responsibilities for Problem-Domain Objects #64. “Attribute with Repeating establishing responsibilities / Values” Strategy what I know (consider and challenge) • An attribute that may have a number of values? • Add a new class to your model. Add an object connection. Look for additional attributes that may apply. Add a new class, even if it has only one attribute for now. Why: make the most of problem-domain partitioning; pave the way for accommodating future change gracefully. • Example: Item with the attribute UPCs. Add a UPC class. Add an object connection between an item and its UPCs. If you potentially could have attributes for each repeating value, then go ahead and split what’s being described as another class in your model. It’s domain-based partitioning. Even if the new class has only one attribute, go ahead and add it anyway. As you find a need for additional attributes and services, you’ll already have this domain-based partitioning in your model. And that’s a good deal. Here, UPC is the repeating value. An item in Connie’s Convenience Store may correspond to many manufacturer-issued UPCs. Could you have potentially many attributes for each UPC? Absolutely. A UPC could be described by its code, its bit-map image, its originator, and its date of first usage. Right now, within this system’s responsibilities, suppose that all you care about is the UPC itself. No matter. Go ahead and add a UPC class, with the attribute “upc.” How about an object connection, too? Yes, you need one. An item knows its UPC objects. And a UPC object knows its items. Connect item and UPC with an object connection (Figure 1-26). Consider price An item object knows many prices. Hey, you don’t believe it? Check it out with Connie! (Peter) Tell me about the prices of an item. (Connie) An item has a regular price, beginning on an effective date; we keep track of past, present, and future regular prices. In addition, an item often has a promotional price, good from an effective date through an expiration date; we keep track of past, present, and future promotional prices. We pride ourselves in giving our customers the best price that applies at the time of purchase. (Peter) Do you plan prices in advance? When would you add them to the system? (Connie) We plan ahead. And we definitely need to enter the new prices in advance of their effective dates. So what does all of this mean to your object model? An item knows its price objects. An item knows its regular prices (with price and effective date). An item knows its promotional prices (with price, effective date, and expiration date).
Establishing Responsibilities for Problem-Domain Objects Connie’s Convenience Store 41 So what should you add to your model? Add a price class, with the attributes: – price – effective date. Add a specialization class, promo price, with the attributes: – price – effective date – expiration date. But wait! A specialization class inherits the attributes, connections, services, and messages that apply to its generalization class. You see, a gen-spec structure communicates “what’s the same; what’s different.” What’s the same: – price – effective date. What’s different: – expiration date. Add it to your model. What about object connections? An item knows its price objects. And a price object knows its item. So connect item and price with an object connection (Figure 1–26): upc UPC 1 n Item number description taxable n 1 price effectiveDate Figure 1–26: Discovering additional objects and responsibilities. On describing each attribute At some point along the way, you might add some descriptive information about each attribute. First things first, however. Pick good attribute names, ones that communicate exceedingly well. A well-chosen name is far more helpful than an abundance of descriptive words. (Hey! And that means if you need a long-winded attribute description, you should find a better attribute name.) Nevertheless, you may want to add attribute descriptions, more fully communicating what each attribute is all about. Price PromoPrice expirationDate
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 19 and 20: Applying Patterns: Select and Organ
Page 29 and 30: Establishing Responsibilities for P
Page 39: 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
Page 67 and 68: Selecting Human-Interaction objects
Page 69 and 70: Establishing Human Interaction Resp
Page 71 and 72: Establishing Human Interaction Resp
Page 73 and 74: Working Out Human-Interaction Dynam
Page 75 and 76: Scenario: actual cashier logs on. S
Page 77 and 78: Scenario: sell item. Receipt SaleLi
Page 79 and 80: Scenario: get payment by check Rece
Page 81 and 82: Selecting System-Interaction Object
Page 83 and 84: Establishing System-Interaction Res
Page 85 and 86: Working Out System-Interaction Dyna
Page 87 and 88: Selecting Data-Management Objects a
Page 89 and 90: Working Out Data-Management Dynamic
Page 91 and 92:
Progress at This Point Connie’s C
Page 93 and 94:
Progress at This Point Connie’s C
Page 95:
Wrap Up Connie’s Convenience Stor
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Connie's Convenience Store - About Peter Coad

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