Planning Extreme Programming - kent beck martin fowler phần 7 doc

Is it bigger than a breadbox?

--20 Questions

Base estimation on finding a similar piece of work that you’ve

already done. It’ll take about the same amount of time as that.

How do you come up with estimates? We’ve seen a lot of words

devoted to this topic. We’ve seen quite a few mathematical formulae.

The best of these are based on the lines of code to be written. These

can tell you how much time it will take to develop so many thousand

lines of code. This is particularly useful since it’s so easy to estimate pre￾cisely how many lines of code a solution will be before you start writing

it. (Spotted the sarcasm yet?)

Let’s be clear, estimation is a black art at best. You’re not going to

get accurate figures however hard you try. You can, however, get good

enough numbers with a little bit of effort, and you can get better num￾bers over time.

There are two keys to effective estimation

✧ Keep it simple

✧ Use what happened in the past

The best guide to estimating the future is to look for something that

happened in the past that was about the same as the future thing. Then

just assume that history will repeat itself, as it often does. If there’s a

significant difference between then and now, then use a very simple way

to factor it in. Don’t try to be too sophisticated, estimates will never be

anything other than approximate, however hard you try.

Chapter 19

Estimation