Architecture Evaluation

During the ICSM presentation of Eric Bouwers about criteria for assessing implemented architectures I asked a question that raised a discussion that was proposed by Yuanfang Cai to be taken off-line. Since I already left Edmonton, I’m taking it on-line instead. There is no doubt Eric has made considerable contribution by analysing SIG expert opinions, reports and interviews, my question was more about the relation between architecture evaluation and architecture evolution and his proposal to integrate regular architecture re-evaluation into maintenance activities.

One of the definition of architecture that I remember from the time working in the same department with Hans van Vliet is that it comprises those components, dependencies, properties, configuration elements, etc—in other words, those parts of a system design that do not change with time or are the most reluctant to change with time. I.e., the easier it is to discard or to change something, the less place it deserves in the architecture. If you think the problem is purely terminological, please direct me to a perfect definition, and I will shut up. However, I believe there are some deeper issues here.

Can architecture re-evaluation be used as a system analysis tool that can deliver useful and non-trivial results?

So far I can imagine three scenarios: (1) the software system evolves without changing its architecture; hence, re-evaluation is redundant since it will provide the same results we already obtained; (2) the software system is redesigned in the meantime in such a way that its architecture changes as well; hence, re-evaluation is needed since we can no longer rely on the outdated data; (3) the software system evolves in such a way that the properties of its architecture can shift without noticing; hence, the answer to the question from the previous paragraph is definitely "YES". The first two scenarios are trivial, the third one is not, and I call for examples. So far I can think of only external ones, like when a new technology is introduced and makes parts of the existing system outdated/obsolete/incompatible/… Are there internal ones?