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three-tier class model that you might find helpful when first learning OOP. The three-tier architecture partitions your application as follows: |
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User Services, which encapsulate the mechanisms for providing interactivity between the user and the application |
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Business Services, which encapsulate the business process logic and serve as a bridge between the user and the information repository (or database) |
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Data Services, which encapsulate the connection between business services and the information repository |
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In this chapter, you learned about the fundamentals of object-oriented programming. At the center of this evolving technology are the class and its runtime equivalent, the object. A class is a design-time template that determines the behavior of objects based on it. Visual Basic enables you to perform OOP, using the class module and the Class Builder utility. |
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The fundamental idea to keep in mind in OOP is that the Visual Basic project must be viewed as a round-trip (or cyclical), evolving process, meaning that the artifacts of the analysis phase will need to be synchronized with the design and construction phases. Without this periodic synchronization process, you will lose the ability to trace the classes you create from the analysis phase down to the construction phase. This is where novice object-oriented programmers, often impatient, become confused and discouraged. When requirements need to be revisited, novice object-oriented programmers can't tell what class corresponds to what entity in the analysis and design models. Traceability, then, is of fundamental importance to object-oriented programming. |
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Day 2 shows you how to discover and evolve class identities from user requirements (even if you, the developer, will be the primary user) into a use-case model that is the foundation for the class model. Day 3 shows you how to iterate/evolve from the analysis phase to the design phase, meaning that you'll learn how to evolve your project from the use case model to the class and object models. Design tools such as Class Builder, Rational Rose/Visual Basic, and Microsoft Visual Modeler are discussed. Finally, Day 4, Fundamental Object-Oriented Programming, teaches you how to make classes and subsystems (class packages) communicate with each other properly. This communication-building process is also associated with the software development (or construction or programming) phase of the project life cycle. |
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