Hitchhiker's Guide to Software Architecture and Everything Else - by Michael Stal

Friday, July 25, 2008

Design Pearls

If you ever have been to Florence, you surely have admired all those incredible ancient buildings fully covered with ornaments. In the past, constructing beautiful buildings has been en vogue. Today, we simply could not afford the costs required for such endeavors.

What holds true for building construction, is also applicable to software development. But software engineers don't consider themselves just as craftsmen, but also as artists. We strive for architectural beauty and aestethic design, not being satisfied with functional aspects.

While architecture beauty is an important achievement, improving qualities such as expressiveness, simplicity or symmetry, design pearls define the other extreme.
By design pearls I am referring to masterpieces of software design which don't stop just meeting the requirements, but also add unnecessary burden (or ornaments if you will) to the system.

While design pearls show the mastership of one single individual they are counterproductive for team development as they decrease simplicity (there are more artifacts than necessary for the given task) and symmetry (they don't follow the KiSS principle but try to constantly reinvent the wheel).

We can avoid design pearls by strictly following a requirements-driven approach. All architecture concepts in a system must be rooted in a concrete requirement. In addition, we should use patterns where useful. A pattern is a "complete disregard of originality". It just helps reusing common wisdom, instead of coming up with new solutions. And we should strive for architecture quality indicators such as simplicity, expressiveness, orthogonality and symmetry. One way to aim for symmetry is to introduce design guidelines from day 1. Instead of letting developers figure out how to cope with cross cutting concerns such as exception handling, it is better to give them a framework of rules and guidelines.

In summary: design pearls are really nice to look at but ugly to change and extend.


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