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Planning Extreme Programming by Martin Fowler, Kent Beck

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Chapter 7. Four Variables

 

I canna change the laws of physics. I've got to have thirty minutes, Captain.

 
 --Scottyk, Star Tre
  • We use four variables to help us think about how to control a project: cost, quality, time, and scope. They are interrelated but affect each other in strange ways.

We've all heard statements like "Cost, time, quality: pick any two." Plenty of people have ways in which they talk about how there are these variables involved in getting something done, and that you can't control them all at once. In planning software projects, we had to add a variable before we could bring our projects under control:

  • Cost

  • Quality

  • Time

  • Scope

We like to think of them as four levers on some big Victorian steam machine. The four levers control the machine ...

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