## Wednesday, April 23, 2008

### The art of software estimation

I'm reading up even more on the Cocomo II method and interestingly, I like it. Although it's all maths and you can't run companies through formulas of course, the exercise you're put through is the real value.

Consider the following definitions of estimate:
"to judge size, amount, value etc, especially roughly or without measuring"

"to form an idea or judgement of how good etc something is"

"a calculation (eg of the probable cost etc of something)"
So estimating is about forming ideas, judging and calculation. Cocomo II does just that. No estimate method can replace the judgement part, but it can provide the math part.

There are loads of parameters to consider, but within the context of a formula you get an idea what their impact is when you deviate by some values. For example, some parameters only slightly add cost and time, whereas others have a strong exponential factors and an incorrect evaluation of the real value has great consequences.

One of those factors is regarding re-use. For regular projects I worked in, people wouldn't properly go through the practice of estimating the re-usability of some piece of software. Clean interfaces, excellent documentation and little coupling with a used library means it can plugged in within one day or so. But once you plug in a library that has good documentation, probable bugs, but controls your software (like Spring), the effort of integrating and configuring it into your code suddenly becomes a lot larger. Unfamiliarity with the business sector, the library code, other packages and how they work together also adds up linearly to that effort.

There's a great opportunity here for a new opensource tool on the web that supports these kinds of estimates. And it has to be written for the non-cocomo savvy users. Estimating with Cocomo only really makes sense once you are working in teams of 3 or more for 3 or more months. Anything before that is probably better off with a hand-written estimate on a piece of paper, because the size isn't considerable at all. However, be aware that the accuracy very quickly wears off after that and you need to be put through a real practice of estimation. It's really an art form, but nothing mystic, just common sense. And I think anyone will produce incorrect estimates. As long as you understand by how far you could be wrong and supply that value along with the estimate.

For Project Dune, I intend to make something quite easy. The idea is to explain the purpose of the parameters and allow the user to tweak them. Then on a side-bar show a real-time graph with the impact of the changes. And everything in a kind of wizard form.

Estimates are based mostly on code size. And size can be expressed in either Lines Of Code or Functional Points Analysis points. Then you should use a multiplication factor and apply the formula and out comes your cost and timeline.

As said before in the previous post, I wouldn't be so much interested in the actual estimate produced, but much more so in the potential variance. Probably with some more maths behind it, there should be a possibility to show range graphs that indicate the very worst case, the likely bad case, the real estimate, the likely good case and the best case.

The estimate is used as input to project planning. It doesn't yet adjust for serial / parallel work breakdown structures. So the real planning that states "how long" a project takes is still different. You may have people idling or crashing tasks to get things done.

I'm sure there's more stories on estimation at a later time in this blog.