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Understanding First Principles

Advocates of Emergent Design sing the praises of cohesion, coupling, focus and redundancy.

“If you have a hammer and a screwdriver in your toolbox, the question is not what tool you should use, but what problem you want to solve,” remarked Net Objectives CEO Alan Shalloway in his Monday morning tutorial, “Emergent Design: Refactoring and Design Patterns For Agile Development,” at SD West 2003 in Santa Clara, Calif. Shalloway and his co-presenter Scott Bain sought to answer the question: What does it take to design good software? Both presenters advocate the Emergent Design approach, based on agile principles: Understanding the problem as you’re trying to solve it, requiring developers to embrace, rather than resist change. According to Shalloway, “You have to step back and see things that neither you nor your customer will ever think of, and the ability to think in patterns will help.”

To do this, sufficient but not excessive methodology must be in place—an agile approach allows developers to respond to the changes in the project. Shalloway outlined agile principles, explaining that though an agile approach won’t necessarily truncate development time, it will give the customer what he wants: “Agility creates more work (more tests), but saves time later in finding errors in your system,” he explained.

Shalloway then enumerated the “first principles” of good software design:

Redundancy: There should be none.

Shalloway admitted that these ideals are reminiscent of the analyst’s advice to “buy low and sell high,” so he used the rest of the session to describe methods of pinning down abstractions into practice with unit testing, along with refactoring and coding standards.

Why test before coding? Class testing, Shalloway noted, is a demonstration of knowledge that confirms you’re on the right track. Testing success largely depends on how well the first principles are implemented: The test-change-test-again methodology helps to re-enforce refactoring tenets (cleaning up bad code and accommodating changing requirements). Other vital practices aim at eliminating redundancy; employing exception handling, commonality and variability; identifying and encapsulating code variance; and promoting composition over inheritance. Finally, Shalloway added, pattern-oriented development allows developers to ignore the details while promoting proper interfaces to classes.

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