22.tex

Architectural Tradeoffs

Every software architect should know and understand that you can't have it all. It is virtually impossible to design an architecture that has high performance, high availability, a high level of security, and a high degree of abstraction all at the same time. There is a true story which software architects should know, understand, and be able to communicate to clients and colleagues. It is the story of a ship called the Vasa.

In the 1620's Sweden and Poland were at war. Wanting a quick end to this costly war, the King of Sweden commissioned the building of a ship called the Vasa. Now, this was no ordinary ship. The requirements for this ship were unlike any other ship of that time; it was to be over 200 feet long, carry 64 guns on two gun decks, and have the ability to transport 300 troops safely across the waters into Poland. Time was of the essence, and money was tight (sound familiar?). The ship architect had never designed such a ship before. Smaller, single gun deck ships were his area of expertise. Nevertheless, the ship's architect extrapolated on his prior experience and set out designing and building the Vasa. The ship was eventually built to specifications, and when the eventful day came for the launch, the ship proudly sailed into the harbor, fired its gun salute, and promptly sank to the bottom of the ocean.

The problem with the Vasa was obvious; anyone who has ever seen the deck of a large fighting ship from the 1600's and 1700's knows that the decks on those ships were crowded and unsafe, particularly in battle. Building a ship that was both a fighting ship and a transport ship was a costly mistake. The ship's architect, in an attempt to fulfill all of the kings wishes, created an unbalanced and unstable ship.

Software architects can learn a lot from this story and apply this unfortunate event to the design of software architecture. Trying to fulfill each and every requirement (as with the Vasa) creates an unstable architecture that essentially accomplishes nothing well. A good example of a tradeoff is the requirement to make a Service-Oriented Architecture (SOA) perform as well as a point-to-point solution. Doing so usually requires you to bypass the various levels of abstraction created by an SOA approach, thereby creating an architecture that looks something like what you would typically order at your local Italian restaurant. There are several tools available to architects to determine what the tradeoffs should be when designing an architecture. Two popular methods are the Architecture Tradeoff Analysis Method (ATAM) and the Cost Benefit Analysis Method (CBAM). You can learm more about ATAM and CBAM by visiting the Software Engineering Institute (SEI) websites at http://www.sei.cmu.edu/architecture/ata_method.html and http://www.sei.cmu.edu/architecture/cbam.html respectively.

By Mark Richards