Connie's Convenience Store - About Peter Coad

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14 Connie’s Convenience Store Selecting Problem-Domain Objects (Note: a register consists of a number of data entry devices: a mag stripe reader, an item scanner, a keypad, and a receipt printer. You don’t need these in your object model; all of these are just data entry device “nuts and bolts.”) Kinds of things, too You might be interested in categories of items, such as: – perishability: perishable, nonperishable – taxability: taxable, nontaxable – type: dairy, produce, canned goods, frozen foods. Should you add some additional classes, representing these different kinds of items? Here’s how. For each category, consider the following: – If you don’t care about the distinction, forget about it. – If all you care about is the category value, add an attribute. – If a category implies added attributes, then add a specialized class; put the added attributes in it. – If a category implies different services, then add a specialized class; put the added services in it. In this case, based upon the system features, you don’t really care about the distinctions. Just add item, for now. Descriptive things #19. “Select Items and Specific Items” Strategy selecting objects (pattern players) • Look for items, descriptive objects with values that apply to some number of specific items and actions that apply across those specific items. • Examples: aircraft–specific aircraft, loan description–specific loan, job description–specific job, video description–videotape, price category item–specific item, tax category item–specific item. What kinds of catalog descriptions or descriptive tables of values do you need to do business? In this system, it’s tax tables. Yuck! Anyway, you really do have to keep track of tax categories, and the taxable rate that applies for each one. Add a tax category object, so you can keep track of each category, its rate, and its effective date. Add your “tangible things” and “descriptive things” to your object model (Figure 1–6):
Selecting Problem-Domain Objects Connie’s Convenience Store 15 ProblemDomain CashDrawer Cashier Item Person Register Item Register Store TaxCategory TaxCategory CashDrawer Figure 1–6: Select tangible things and descriptive things. About transactions as things What’s a transaction, in the context of building an object model? A “transaction” is a recording or logging of any event of significance; hence, you could call it “a significant event remembered.”A “transaction object” knows about a significant event, knows who the players are in that event, and calculates things pertaining to that event. #17. “Select Transactions” Strategy selecting objects (pattern players) • Look for transactions, “events remembered,” events that the system must remember through time. A transaction is a moment in time (for example, a sale) or an interval of time (for example, a rental). • Look for an entry in a historical record or log, an entry that must be maintained. Why? To answer questions or to perform assessments. • Examples: agreement, assignment, authorization, contract, delivery, deposit, incident, inquiry, order, payment, problem report, purchase, refund, registration, rental, reservation, sale, shift, shipment, subscription, time charge, title, withdrawal. • Note: Nearly all transactions consist of a number of transaction line items. • Note: Where do these transactions come from? The possibilities are: A window (the event logged is based upon human interaction at some point in time) Another object, monitoring for a significant event, then logging that such an event occurred Another system, one that your system can interact with regarding events it logs. So the question is: what are the transactions, the notable events that must be recorded by your system? Consider Connie’s Convenience Store. What significant transactions, events remembered, occur every day? How about: – sale – payment (a companion to any sale at Connie’s) – session (from logon to logoff).
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 13: 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
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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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Connie's Convenience Store - About Peter Coad

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