Summary
In his recent post, Bill Venners included a terrific quote from Ken Arnold. It crystallized my thinking on subjects as diverse as API design, interface design, and documentation (which many developers don't realize, is almost purely a design activity).

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In Bill Venner's post on URL management in Rails, Ken Arnold was quoted as saying:

(Many developers) think from the implementation out, instead of thinking from the user in.

That is pure gold. It nicely encapsulates a variety of issues I've noticed, including documentation, API design, and interface functionality.

To transform that wonderful observation into a golden rule, I'd say:

Think from the user in, rather than from the implementation out.

The impacts:

• Documentation: Describe how to drive the car, not how the steering system works. It's astonishing how many developer-authored whitepapers do the latter. That's good stuff for the design document, and something that other coders will want to hear. But 95% of the people who are looking at your stuff want to use it.
   
• APIs: Design the best APIs you can think of. Do something else for a week. Then write some test applications from memory. When there's a difference between what you thought the API was as a user and what you thought it should be as the designer, favor the user perspective. Rename the API or refactor to match the way you thought it would work when you were using it. Whenever possible, build your application tests first.
   
• Interface design: Don't build an interface for your technology, so it can be used. Build an interface that solves user problems. Set up use cases and design an interface that minimizes the number of steps the user has to take in the most frequent use cases, that makes less common cases possible, and that above all makes it easy to remember how to do things. Then use your technology to implement it. And if the APIs get in way, change the APIs!

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About the Blogger

Eric Armstrong has been programming and writing professionally since before there were personal computers. His production experience includes artificial intelligence (AI) programs, system libraries, real-time programs, and business applications in a variety of languages. He works as a writer and software consultant in the San Francisco Bay Area. He wrote The JBuilder2 Bible and authored the Java/XML programming tutorial available at http://java.sun.com. Eric is also involved in efforts to design knowledge-based collaboration systems.