Dissection of an Application Framework - The Framework Development Process
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After you have decided that you need an application framework, you should first determine the major phases involved in a framework development process. Figure 2-2 shows four majors phases: analysis, design, development, and stabilization.
Figure 2-2. Framework development process
The gray inner circle indicates the phase, and the outer circle indicates some of the major tasks involved in each phase. Let’s take a look at what is involved in each phase.
Analysis
As we start the process of developing an application framework, the first phase we enter is the analysis phase. As with application development, framework development starts by first setting the scope and objectives of the project or framework. We need first to identify the key features that are to be included in the framework. What types of business applications will be relying on this framework? What use cases will the framework support? In other words, how will developers be able to develop their business applications on top of this framework? The framework is built to support the development of the business application, so it is important to figure out what business domains the framework will able to support. Many questions will be asked during the analysis phase of framework development to set the scope and objectives of the framework.
During the analysis phase, we also need to create an iteration plan for improving the framework over time. Framework development involves complex and abstract tasks, and you shouldn’t expect to get everything right on the first iteration. You may discover that certain items need to be added to or removed from the framework as you start implementing it. You may also decide to modify how some parts of the framework work to help developers become more productive in adapting the framework. You need to set up a plan to collect ideas for enhancements and fixes as developers start using the framework for use as the input to the next iteration. In addition to such an iteration plan, you will also need to draft a project plan and establish a timeline and documentation of major milestones for all phases of the process.
Design After we have set the objectives for the application framework, the next phase is the design phase. The design phase for framework development involves two major tasks. First, we need to identity the common spots and the hot spots in both the domain-specific layer and the cross-domain framework layer. Second, we need to devise an architecture for the framework that will be used as a blueprint during the construction phase.
“Common spot” and “hot spot” are special terms relating to framework development. You will learn more about them later in the chapter. In a nutshell, a common spot is an area in the framework where variation is unlikely. A common spot is often a framework component or service that is ready for use without significant customization by application developers. On the other hand, a hot spot is an area in the framework where variation is frequent. Developers must provide their specific business logic in those hot spots in order to use the framework component. A hot spot is an abstract method that requires the developer to implement specific business logic. Identifying the common spots and hot spots in a business application allows you to identify the specific components and services in the framework. Identifying what is variable and what is fixed in a business domain is not an easy task. The business experts and software architects need to work together to identify those spots among the different layers of the framework in order to design a framework that is both easy to use and extensible.
After the business experts and software architects have come up with a list of components and services and identify which are common spots and which hot spots, the software architects can start designing the blueprint of the framework. As part of the architectural design of the framework, you need to create a number of design deliverables, such as class diagrams and activity diagrams, which will be used during the construction phase of the framework. Software architects also spend their time thinking about the techniques they can use on various components and services, such as design patterns, to maximize code reuse and extensibility in the final framework.
During the design phase, you can also begin to create a prototype of the application framework and then build a sample application on top of it. Testing the prototype with a sample application helps you learn how the framework you develop will be used to build the business application and gain insight into potential improvements in the design of the framework.
Implementation After the framework design is done, the next phase is to actually code the application framework. The implementation phase has one goal, which is to develop a framework that meets the requirements and time constraints. If you have done a good design job on the framework, implementing it is no different from regular application development. As with application development, where different team members can work on different parts of the same application simultaneously, you can have work progressing on different pieces of the application framework simultaneously, as long as the framework is partitioned into well-defined modules. Unit testing on the newly created functionality can be tricky during framework development. In the case of application development, developers will simply test the use case on the newly created functionality to see whether it works as desired. However, unit testing of frameworks is much less direct and visual than that of business applications, since the application that uses the framework simply hasn’t been created yet and all the business data needed by the application have not been generated.
As with application development, you can create number of milestone releases during the implementation phase. You can create several incremental releases so that you can get part of the application framework to developers and start getting feedback on any potential improvements and fixes for the next release.
Stabilization The stabilization phase, the last phase before the next iteration starts, focuses on testing, bug fixing, developer feedback, documentation, and knowledge transfer.
Testing the framework in this phase is often driven by developers instead of professional quality-assurance testers or business end users, since developers are the primary users of the framework. During the stabilization phase of the framework development, the design and construction of the actual application have not yet started, so developers haven’t yet created much application code. In such a situation, you need to identity at least one usage scenario in the business application for each framework component and service and ask the development team to write a small portion of the application based on such usage scenarios. Although it is not possible to test every framework usage scenario of an application that has not yet been built, you can effectively test your framework through the selective implementation of part of a business application that is representative of the usage pattern of the framework.
Of course, in order for developers to develop part of an application based on the framework, they must know how to use the framework productively. As the creator of the application framework, you will initiate developer training in the stabilization phase. The better job you do educating developers about the framework, the better the developers will be able to test your framework and the more productive they will be when they start using your framework extensively in application development.
Besides conducting frequent training sessions on how to use the application framework, you also need to produce good documentation of your framework, which will be an invaluable tool in helping developers learn to use the framework.
Typical documentation created to help developers consists of four parts:
- An overview of the framework that explains the purpose of the framework and the major components and services available in the framework.
- Some pictures, diagrams, and descriptions of the framework that help developers grasp the framework and its design philosophy.
- An API reference for the functionalities inside the framework that enables developers to look up the framework’s functionalities during the development process.
- A collection of examples that show how the framework is used. Concrete examples of the framework in action best demonstrate the usage scenario of the application framework and help shorten the learning process for developers.
The stabilization phase is also where the framework designer will continually collect developers’ feedback on the framework for the next iteration of framework development. After developers start using the framework, the framework designer must also participate in the effort of application development by providing assistance to the developer team, answering questions and solving problems related to the usability of the framework.
With a development process in place for framework development, let’s look at some common approaches and techniques for developing a framework that we will use in the rest of the book.
 This chapter is from Developing Application Frameworks in .NET by Xin Chen (Apress, 2004, ISBN: 1590592883). Check it out at your favorite bookstore today. Buy this book now.
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