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Component-Based Development
TopCoder Style

Monday, March 17, 2003
By srowen, TopCoder Member

There is programming, and there is software development. You, dear TopCoder member, demonstrate weekly that you can solve well-stated programming puzzles quickly.

Yet solutions to real-world problems require more: deciding *what* puzzles must be solved, describing them thoroughly, developing solutions that are open to change, and verifying those solutions: design, documentation and testing. Together with the actual programming, these make up the software development process.

These are not new issues, and fortunately we have a set of common tools available when tackling these software development tasks. Object-oriented language was a major step forward for design, as was the Unified Modeling Language (UML) for describing software systems. Wide interest in standard "design patterns" has added to designers' common vocabulary of design solutions. Finally, standard open-source unit testing packages like JUnit have helped developers benefit from early and frequent testing.

Despite all this, it's still an art, not a science, and software development skill grows with real experience. Lucky for us then that TopCoder Software has done for software development what TopCoder did for programming, where members can compete to design and develop small software components. It's instructive to see a modern software development process in action on a small scale, and to learn through participation (and of course there is the lure of prize money.)

So, this article presents my own perspective on how to navigate the software *design* process. This being TopCoder, it is in the form of a brief 10-step guide to designing TopCoder Software components, but the ideas should be somewhat applicable elsewhere, since TopCoder Software's practices are common to many Java projects (i.e., Ant, JUnit, javadoc, UML). I hope to convince you that this doesn't have to be a difficult or time-consuming process, and thereby encourage even more TopCoder members to bring their skills to the competition, and also employ these software development processes in the real world. It can only make us all better designers and developers.

1. Pick your component; conceive your approach
At TopCoder Software, start by picking a component that interests you, or pertains to your experience. If you can apply some specialized knowledge or great insight to your design, then it has a real "secret weapon." Winning a design competition is not just about producing good documents, but also presenting a compelling story for the future of the component; think about what in your design will really sell the review board on your ideas. For example, those with a finance background might dream up significant extra functionality for the Financial Calculator; those with extensive networking experience know more about what needs to be designed into the HTTP Tunneling component.

2. Inquire about the component
Inquire about the design competition at so that you can get access to the component specification forum. There you can get the design submission .jar file, which contains the directory structure for your submission. Unpack this into a local directory, and complete whatever other local setup you need. Setting up your environment and organizing your resources is always an important first step.

3. Define your use cases
This should be easy; having considered the component requirements, and decided basically where you want to go, you should be able to list about two to five distinct things that are done with the component, and who or what ("actor") does them. Just consider how you might summarize this informally for another developer. For TopCoder Software components, you may often just have one "actor", which is the software application that uses the component. As an example, what do you do with a Spell Check component? Create and configure it, and use it to find misspelled words in a document? Or possibly, correct misspellings based on suggestions?

Get started on your model in Poseidon: start a new model, and create a use case diagram. Drop in an actor, create a use case bubble for each of your use cases, connect them, done!

4. Prototype it
Conventional wisdom says that one should design first, and implement second. Indeed, that's generally good advice, but it's always tempting to skip right to the coding. In this case, give in - start laying out some of your ideas in code; see if you can get basic functionality working. In the process, you may discover that your conceptual design doesn't actually work out well when it comes to coding it. You may find out that your algorithms, or third-party components you want to use, don't work. A couple rounds of coding should uncover any fatal design problems before you go any further.

5. Write your class diagram
After you have tried out your design ideas in code, and are satisfied that it can be made to work well, you should have a sense of what classes will make up your design, and how they will relate. Start adding these to your class diagram.

TopCoder guidelines and example documents demonstrate exactly what you need to model (essentially, anything public - if there are important non-public elements, though, these can be modeled as well). This is the "map" for your component design, so strive for clarity - the point of the diagram is communication of ideas to another person like yourself. Make the diagram neat; the arrangement of diagram elements should visually communicate groupings. Don't model anything beyond the basics unless you really feel it's important; too much detail can obscure the basic structure.

Fill in javadoc as well according to TopCoder guidelines to the Poseidon diagram; this is the place to detail exactly what each public method and class does.

6. Write sequence diagrams
Sequence diagrams describe the flow of control and information in the component for its various actions. While there are a number of ways to approach sequence diagrams, for small software components, a good rule-of-thumb is to describe functionality at the level of pseudo-code. It will help developers understand to implement functionality at a high level.

What to model and not model here is fairly subjective; again, remember that the purpose is to clearly communicate the high-level structure of the implementation to other developers. Capture all the major method calls and interactions between objects; skip the minor details, as they just clutter the diagram. If the diagram runs past two printed pages or so, it's likely too big - reduce your level of detail, or break the diagram into two if possible.

Sequence diagrams for TopCoder Software components are available on the web site; browse a few to develop a sense of how different designers like to model these items.

7. Fill out the component specification
Having almost perfected the UML documentation of your design, finish by writing up the English documentation. For TopCoder Software, that's the Component Specification document. Like in any design, you should include a concise summary of the component's functionality and major design points. The rest of the document should be straightforward to complete, with your completed Poseidon model. In particular I think it is useful to include illustrative code snippets in section 4.

8. Export skeleton code and add javadoc
With a completed class diagram, you should be able to export skeleton Java code from Poseidon. You will need this code when writing your test cases. Fill in javadoc as well according to TopCoder guidelines to your skeleton code; this is the place to detail exactly what each public method and class does. Be sure to follow TopCoder's code formatting guidelines, which are basically Sun's guidelines; these are commonly used in Java projects as well.

9. Write test cases
Writing test cases before coding starts is gaining popularity as an effective way to empower developers to write good code; for small software components it is, without question, feasible, and useful. TopCoder Software enforces this because you, the designer, will write some test cases for the benefit of developers after you.

Your tests verify that the functionality you have specified is provided in an implementation. If you say that a method should not accept null, test for this. Cover all public methods in your tests - this ensures that the tests won't even compile if any part of your API is not implemented. Write tests that verify all basic functionality.

See the example TopCoder design submission for an example of a JUnit test case.

10. Repeat if needed, and submit
You will likely need to revise your work from steps 5 though 9 a few times. It's advisable to step away from your work for a day or so, then review your entire submission with fresh eyes one last time. It's easy to accidentally make updates in one place but not another - for example, if you revised a method's name during design, did you updated it in the class diagram, the skeleton code, the unit tests, and in the component specification?

Once satisfied, build your design submission and send it in!

This approach works well for me in practice at TopCoder Software, and during other real-world software development. It's not the only approach to be sure, nor necessarily the best, but I offer it to new and experienced developers alike as just another perspective "from the field." Cultivating good design habits turns good programmers into powerful software developers; I hope that more of TopCoder's strong programmers will contribute to and learn from participation in TopCoder Software design and development projects.

By srowen
TopCoder Member

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