Connie's Convenience Store - About Peter Coad

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6 Connie’s Convenience Store Selecting Objects #25. “Object-Model Components as a Guide” Strategy selecting objects (model components) • Use object-model components as a working outline for organizing your search for objects. • PD: problem domain HI: human interaction DM: data management SI: system interaction (and NT: not this time). Each class fits into just one of these model components. Why use model components? Use them to partition the classes into meaningful, loosely coupled subsets. Here’s an overview (Figure 1–2) of how it works: WINDOWS kslzm lalz o a.kk alf iekl a;flki klcli a tl f iksliadj' lkdsfos ek li akdo l;e;ils kslzm lkfoek lalz o a.kk aodir lalo alf iekl akdo a;flki gol klcli a tl tola fo f ejap iksliadj' mane lkdsfos ae ek li akdo l;e;ils lkfoek aodir lalo akdo gol tola fo ejap mane ae REPORTS tola jfdoaleokj s skfo elacnma afot kamdm z htislj lsf tola a pao jfdoaleokj akidl azk s skfo l elacnma majdio afot akdo kamdm a z the alid htislj apa lsf to a pao balon aldoej akidl azk sa l gamm majdio aoe lweakdo a the alid apa to balon aldoej sa gamm aoe lwe HumanInteraction ProblemDomain DataManagement DISK Files RDBMS ODBMS SystemInteraction Figure 1–2: Object model components and their interactions. The problem-domain (PD) component contains the objects that directly correspond to the problem being modeled. Objects in this component are technology-neutral. They have little (or no) knowledge about objects in the other components (human interaction, data management, and system interaction). The human-interaction (HI) component contains objects that provide an interface between problem-domain objects and people. In an object model, such objects most often correspond to specific windows and reports. The data-management (DM) component contains objects that provide an interface between problem-domain objects and a database or file-management system. In an object model, such objects most often correspond to specific problem-domain objects that need support for persistence and searching. The system-interaction (SI) component contains objects that provide an interface between problem-domain objects and other systems or devices. A system-interaction object encapsulates communication protocol, keeping its companion problem-domain object free of such low-level, implementation-specific detail. OTHER SYSTEMS DEVICES
Selecting Problem-Domain Objects Connie’s Convenience Store 7 That’s four object-model components. There is a fifth one. It’s the “not this time” component. It’s a bucket that holds objects that are interesting, ones that you consider, yet that for one reason or another (be it technical, sociological, or economic), you’ve decided not to include at this time. By using this component along with the others, you can show what’s included—and what’s not. By organizing classes this way, you facilitate simpler modeling this time (within each model component). You also increase the likelihood of reuse next time. Why? Here’s an example. Next time, you might want to reuse certain problem domain classes, even though you may choose to work with different human interaction classes. What’s the alternative? Smash the model components together. But then the overall model is harder to understand; and in the future, unless you choose the same problemdomain, human-interaction, data-management, and system-interaction approach, reuse is very unlikely. Ouch! So, use model components. Use them as an overall outline, a guide for selecting objects. And use them to keep your classes well-organized, for understanding, and for reuse (Figure 1–3): ProblemDomain HumanInteraction SystemInteraction NotThisTime Figure 1–3: Model components. You can use these model components to organize your approach to building the model. In this chapter, you’ll go from PD to HI to DM to SI. In each case, you’ll use strategies and patterns to help you: – select objects – establish responsibilities – work out dynamics with scenarios. SELECTING PROBLEM-DOMAIN OBJECTS DataManagement Take a walk on the wild side inside Connie’s Convenience Store. Look for objects, one that the system might need to know or do something about. Coming up, you’ll apply strategies for selecting objects: – actors and participants – places – things. For now, consider PD objects. (Later in this chapter, you’ll consider HI, DM, and SI objects, too.)
Page 1 and 2: GETTING STARTED 1 Connie’s Conven
Page 3 and 4: Identifying System Purpose and Feat
Page 5: Selecting Objects Connie’s Conven
Page 9 and 10: Selecting Problem-Domain Objects Co
Page 19 and 20: Applying Patterns: Select and Organ
Page 29 and 30: Establishing Responsibilities for P
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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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Connie's Convenience Store - About Peter Coad

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