Thursday, October 12, 2006

The Swedish Ship Vasa

In the 1620s, Sweden and Poland were at war and the King of Sweden determined to put a swift end to it. Gustavus Adolphus commissioned a new warship, the likes of which had never been seen before. The Vasa shown in the figure was to be the world’s most formidable instrument of war: 70 meters long, able to carry 300 soldiers, and with astonishing 64 heavy guns mounted on two gun decks. The king, seeking to add overwhelming fire power to his navy to strike a decisive blow and shortened the war, insisted on stretching the Vasa’s armaments to the limits. Her architect, Henrik Hybertsson, was a seasoned Dutch shipbuilder with an impeccable reputation, but Vasa was beyond even his broad experience. Two-gun-deck ships were rare, and none had been built of the Vasa’s size and armament.

Like all architects of the systems that push the envelope of experience, Hybertsson had to balance many concerns. Swift time to deployment was critical, but then so were performance, functionality, safety, reliability and cost. He was also responsible to a variety of stakeholders. First of all, in this case, the customer really was King. But Hybertsson also was responsible to the crew that would sail his creation. Also like all architects, Hybertsson brought his experience with him to the task. In this case, his experience told him to design Vasa as though it were a single-gun-deck ship and then extrapolate, which was in accordance with the technical environment of the day. Faced with perhaps an impossible task, Hybertsson had the good sense to die about an year before the ship was finished.

The project was completed to his specifications, however, and on Sunday morning, August 10, 1628, the mighty ship was ready. She set her sails, waddled out into Stockholm’s deep-water harbor, fired her guns in salute and promptly rolled over. Water poured in through the open gun ports, and the Vasa plummeted. A few minutes later her first and only voyage ended 30 meters beneath the surface. Dozens among her 159-man crew drowned.

Inquiries followed, which concluded that the ship was well built but “badly proportioned”. In other words, its architecture was flawed. Today we know that Hybertsson did a poor job of balancing all the conflicting constraints levied on him. In particular, he did a poor job of customer management (not that anyone could have fared better) and acquiesced in the face of impossible requirements.

The story of Vasa, although 370 years old, well illustrated the architecture business cycle: Enterprise goals beget requirements, which begets an architecture, which begets a system. The architecture flows from the architect’s experience and technical environment of the day. Hybertsson suffered from the fact that neither of those were up to the task before him.

Our goal is to give architects another way out of their design dilemmas than the one that befell the ill-faced Dutch ship designer. Death before deployment is not nearly so admired these days.



Source: Software Architecture in Practice

--- Len Bass, Paul Clements, Rick Kazman

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