by John Smith, Rational Strategic Services Organization, International Branch.
John Smith has 33 years experience in engineering, software development, and management. He's worked for Rational Software for eight years, including two years working with the Rational Unified Process (RUP) development team in Vancouver, Canada. He's now with the International branch of Rational's strategic Services Organization in Australia.
Labeling RUP as heavyweight and XP as lightweight without further qualification does both a disservice by obscuring what each is and what each was intended to do. And, when done in a pejorative way, it's simply meaningless posturing. It is the implementations of these as processes that will be either "heavyweight" or "lightweight", and they should be as heavy or light as circumstances require them to be.
XP is not a free form, anything goes discipline-it focuses narrowly on a particular aspect of software development and a way of delivering value, and is quite prescriptive about the way this is to be achieved.
RUP's coverage is much broader and just as deep, which explains its apparent "size". However, at the micro level of process, RUP occasionally allows and offers equally valid alternatives, where XP does not; for example, the practice of pair programming, which is required by XP. This is not intended as a criticism of XP; simply an illustration of how XP, as its name implies, has narrowed its focus.