Connie's Convenience Store - About Peter Coad

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86 Connie’s Convenience Store Selecting Data-Management Objects and Resposibilities Scenario: authorize payment Here is the scenario view (Figure 1–60): Check authorize getAuthorization AuthorizationServer AuthorizationSystem getAuthorization getAuthorization authorize check.authorize ( ; result) getAuthorization AuthorizationSystemSI connect authorize disconnect connect authorize disconnect Figure 1–60: The “authorize payment” scenario view. SELECTING DATA-MANAGEMENT OBJECTS AND RESPONSIBILITIES Data-management (DM) objects are an important part of an object model. Scenario: authorize payment. Scenario constraints: 5.0 seconds, 9 out of 10 times, 20.0 seconds max. authorizationServer.getAuthorization (check ; result) authorizationSystem.getAuthorization (check ; result) authorizationSystemSI.connect (; result) authorizationSystemSI.authorize (; result) authorizationSystemSI.disconnect (; result) #32. “Select Data Management Objects” Strategy selecting objects (model components) • Add a DM object for each problem-domain class of objects that you want to be persistent—stored between program invocations. • Why: use data management (DM) objects to encapsulate search and storage mechanisms across all of the objects within a problem-domain class. • Examples: cashier DM, sale DM, sale line item DM, item DM. Each DM class has just one object in that class. That object knows its corresponding PD objects, and is responsible for taking care of the data management needs across that collection of objects. Here’s what DM objects know and do: – Each DM object knows all of the objects in a corresponding problemdomain class. For example, a cashier DM object knows about all of the cashier objects. – Each DM object knows how to search. You can ask it to search for objects that you need. – Each DM object knows how to load and save. It loads and saves the problem domain objects it knows about. It usually does this if the underlying storage mechanism is not objectoriented.
Selecting Data-Management Objects and Resposibilities Connie’s Convenience Store 87 So why are DM objects so doggone important? – A DM object knows how to store and retrieve objects from whatever storage mechanism is to be used, whether flat file, indexed, relational, or object-oriented. – A DM object isolates data management complexities from the rest of the application. It interacts with local data management facilities and storage devices. When necessary, it interacts with an object that represents another system, to find objects located on an interacting system. – A DM object isolates the transition from an object oriented environment to a nonobject-oriented environment – And in systems that need such capability, a DM object could cache results when an interacting system is down. For searching If an object needs to search across all the objects in a class, and if no domain-based collection can be found to hold those objects, then let the object send a message to a DM object, asking it to do the search. For persistence This point-of-sale system also needs for some of its objects to be persistent, remembered over time, from one execution of the system to the next. Here’s the approach. If the underlying storage management is not object-oriented, then add a DM object for each class with objects that need to be persistent. In this system, just add these DM objects: – person DM – cashier DM – item DM – register DM – cash drawer DM – sale DM – sale line item DM – session DM – store DM – tax category DM – upc DM – price DM – payment DM. Each DM object knows its corresponding PD objects.
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GETTING STARTED 1 Connie’s Conven
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Identifying System Purpose and Feat
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Selecting Objects Connie’s Conven
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Selecting Problem-Domain Objects Co
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Applying Patterns: Select and Organ
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Establishing Responsibilities for P
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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
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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: Working Out System-Interaction Dyna
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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