ThoughtWorks put together a PDF eBook on estimation in agile projects.It starts of with a reprinting of myPurposeOfEstimationbliki, then includes essays on how to estimate both using story points and counting stories.
We see so much emotional discussion about software process, design practices and the like.Many of these arguments are impossible to resolve because the software industry lacks the ability to measure some of the basic elements of the effectiveness of software development.In particular we have no way of reasonably measuring productivity.
You can't put ten pounds of shit into a five pound bag
-- Anyone who has tried
When Kent and I wrote Planning Extreme Programming, we included this whimsical quote to help get the essence of what planning is about.
Many people belive that you can't do a fixed price contract in an agile project.Since the whole point of an agile process is that you cannot predict the future, this isn't an unreasonable supposition.However this doesn't mean you can't come up with a fixed price agile contract, what it really means is that you can't come up with a fixed scope contract.
Many companies like the idea of writing a contract that fixes scope and price because they think it lowers their risk.The mirage says that their financial obligation is fixed at the price of the deal.If they don't get satisfactory software, then it won't cost them.
My first encounter with agile software development was working with Kent Beck at thedawn of Extreme Programming.One of the things that impressed me about that project was the way we went about planning.This included an approach to estimating which was both lightweight yet more effective than what I'd seen before.Over a decade has now passed, and now there is an argument amongst experienced agilsts about whether estimation is worth doing at all, or indeed is actively harmful .I think that to answer this question we have to look to what purpose the estimates will be used for.
I've heard a couple of questions recently about coming up with a standard story point mechanism for multiple teams using extreme programming's planning approach.The hope is have several teams all using equivalent story points, so that three story points of effort on one team is the same as on another.
I think trying to come up with this at best of limited value, and at worst dangerous.
Story counting is a technique for planning and estimation.Similarly toStoryPointsit works withXpVelocityto help you figure out how many stories you can deliver in a fixed period of time.It differs, however, in that you just consider the number of stories per unit of time and (mostly) ignore their relative sizes.
Story points are a common name for sizing stories in agile projects.Combined withXpVelocitythey provide a technique to aid planning by providing a forecast of when stories can be completed.
如果您正在使用XP风格规划,你需要 rapid consensus estimates from developers.Throwing the estimates lets you quickly tell when developers have same similar views on an estimate (so you can note it and move on) or if there is disagreement (when you need to talk about theUserStoryin more detail.
Velocity is a notion that helps calibrate a plan by tying broad statements of effort into elapsed time.Velocity is a statement of how much stuff a team (or a person if it's personal velocity) gets done in a time period.You should usually determine velocity by measuring how much got done in past periods, following the principle ofYesterdaysWeather.A typical approach is to average the velocity the past three time periods to determine velocity for future time periods.Velocity was originally formed as partExtremeProgrammingbut has since spread and is now used widely inagile software developmentof all flavors.
This is the principle that says you'll get as much done today as you got done yesterday.In iterative projects it says that you should plan to do as much this iteration as you did last iteration.The term comes from the Extreme Programming community.