A Unified Theory of Software Evolution

jso888 writes "Salon has a nice article today on Meir Lehman's work on how software evolves and is developed. Lehman's investigation of the IBM OS/360 development process became the foundation for Brooks' Law: "Adding manpower to a late software project makes it later." He is hopeful that his work will make software development less of an art and more of an engineering science."

Comments

The key point is paragraph 9

[gelfling]

"Unless IBM programmers had suddenly figured out a way to write error-free code -- an unlikely assumption -- Lehman made a dire prediction: OS/360 was heading over a cliff. IBM, in stressing growth over source-code maintenance, would soon be in need of a successor operating system."

Which means that commerical systems don't so much evolve as stub their growth paths out and switch direction or spawn new generations because embedded complexity has killed off the feasibility of maintaining it. In other words, all new releases are the cause of and ultimately an attempt to escape from, the chimera that is overly complex code. In commercial terms this should be astounding. We're paying to gronk up our own because we erroneously believe the NEXT version will be something radically new and elegant which of course it can't be.

New Version "x+1.y" is simply an ejection seat.

Open source

[bunyip]

From the article:

Michael Godfrey, a University of Waterloo scientist, is equally hesitant but still finds the Lehman approach useful. In 2000, Godfrey and a fellow Waterloo researcher, Qiang Tu, released a study showing that several open-source software programs, including the Linux kernel and fetchmail, were growing at geometric rates, breaking the inverse squared barrier constraining most traditionally built programs. Although the discovery validated arguments within the software development community that large system development is best handled in an open-source manner, Godfrey says he is currently looking for ways to refine the quantitative approach to make it more meaningful.

It would have been interesting had they delved deeper into this finding. Yeah, I know, the true believers in open source all feel superior (we are, aren't we?), but exploring the reasons why it works would be interesting.

Is it the large-scale peer-review process? Is it that we occasionally rewrite parts (filesystems, VMM, etc)? Something else?

You're missing two premises

[alispguru]

IBM missing premise:

Some of our applications must have 99.999% uptime. Therefore, the whole system must be designed with this in mind.

Microsoft missing premise:

If our applications crash, it's no big deal. Feature lists generate revenue, so that's what we do.

Just making explicit what you said implicitly...