Salon.com: A Unified Theory of Software Evolution

“The pile, a collection of recently published papers
investigating the topic of software evolution, a topic Lehman
helped inaugurate back in the 1970s, is something of a taunting
tribute. Written by professional colleagues at other universities,
each paper cites Lehman’s original 1969 IBM report documenting the
evolutionary characteristics of the mainframe operating system,
OS/360, or his later 1985 book ‘Program Evolution: Processes of
Software Change,’ which expands the study to other programs. While
the pile’s growing size offers proof that Lehman and his ideas are
finally catching on, it also documents the growing number of
researchers with whom Lehman, a man with dwindling office space and
even less in the way of support, must now compete.

“‘And to think,’ says Lehman, letting out a dry laugh. ‘When I
first wrote about this topic, nobody took a blind bit of

“Software evolution, i.e. the process by which programs change
shape, adapt to the marketplace and inherit characteristics from
preexisting programs, has become a subject of serious academic
study in recent years. Partial thanks for this goes to Lehman and
other pioneering researchers. Major thanks, however, goes to the
increasing strategic value of software itself. As large-scale
programs such as Windows and Solaris expand well into the range of
30 to 50 million lines of code, successful project managers have
learned to devote as much time to combing the tangles out of legacy
code as to adding new code. Simply put, in a decade that saw the
average PC microchip performance increase a hundredfold, software’s
inability to scale at even linear rates has gone from dirty little
secret to industry-wide embarrassment…”


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