[readthenotes1]

A major factor supporting evolution over big up-front design is the drift in system requirements over time. Even on large military like projects, apparently there's "discovery"--and the more years that pass, the more requirements change.

[zppln]

This isn't my experience. Requirements tend to settle over time (unless they're stupidly written). Users tend to like things to stay the same, with perhaps some improvement to performance here and there.

But if anything, all development is the search for the search for the requirements. Some just value writing them down.

[readthenotes1]

Iirc, there is a quote from Barry Boehm, author of Software Engineering Economics, who said something in the effect of "I wish you hadn't persuaded me that requirements didn't change much in big military contracts"

They do change, especially if projects take years.

Not only do people tend not to read, or read well, there is a lot on inherent ambiguity in english--so even if not written stupidly there may be surprises.

"Requirements" changed on just about every project I was on. I remember once asking the business owner if he could simplify some requirements cuz they were really complicated to develop well, and he replied Certainly--he was trying to put out something he thought would be easy for us to build.

[sigbottle]

Completely irrelevant but this exchange reminded me of two Greek philosophers saying "everything is change" versus "nothing ever changes" LOL

[YZF]

Even if the requirements are indeed fixed your understanding of the problem domain evolves.