UML Weekend Crash Course™ - To Parent Directory

20
Friday Evening
Extreme Programming
Extreme Programming (XP) shocked a lot of people, including myself, when it first showed
up. The goal of XP is much like that of CRC (that is, keep it simple). This is not surprising
when you learn that the originator, Kent Beck, was also instrumental in the CRC method. XP
does not advocate the UML. I present it here because the goal of this session is to provide
you with an understanding of the diversity of methodologies and the views or attitudes that
various methodologies hold toward the application of the UML standard.
XP strives to strip away anything that is not essential. XP requires a complete and unwavering
commitment from the clients to work side-by-side with the programmers. Working
through stories or scenarios of how the system should work, the teams eventually develop
the entire system. Every iteration of the project (typically one to four weeks each), the
teams deliver something functional. The minimum deliverable is a set of tests.
XP basically says that the code is everything, so there is a very heavy emphasis on coding
standards and design principles. The process includes numerous standup meetings to
keep everyone on the same page. Furthermore, programmers work in pairs so that they can
learn from one another, provide insights, share design alternatives, and generally help each
other out.
Because XP is completely devoted to the code, there is very little use of up-front modeling.
If modeling is used, it is usually thrown away when a decision is reached. XP does use
the CRC method because of its simplicity and utility. Instead of design up front, the method
encourages design through integration and refactoring. In other words, XP advocates believe
that as you learn more about the code, you are in a better position to make the design
decisions and update your code. In one sense, it could be seen as bottom-up design.
Strengths of XP
XP is the first that I know of that truly cared about the programming environment
and its affects on the participants. The bibliography for Extreme Programming
Explained, Embrace Change, by Kent Beck, reads more like a sociology text than a
programming text. No one since Tom DeMarco, writing the book Peopleware, has
devoted as much time to finding ways to make the programming job livable.
XP encourages an extremely close relationship between clients and developers.
XP faces the fact that change is inevitable and often uncontrollable and builds that
fact into the development approach.
Kent Beck has been brave enough to describe what it really takes to create a highcaliber
development environment instead of bowing to the status quo of impossible
deadlines, inadequate user involvement, ill-defined requirements, and programmer
isolation.
Weaknesses of XP
XP relies heavily on setting up the ideal development environment. It starts from
several questionable assumptions:
Highly committed clients will spend huge amounts of time working side by side
with programmers. In my experience, projects are lucky to get access to true subject
matter experts because they are considered too valuable to release from their
current responsibilities.