XP được thiết lập dựa trên bốn nguyên tắc sau: Trao đổi (Communication): XP chú trọng việc trao đổi thông tin một cách 'trong suốt' giữa các thành viên trong nhóm phát triển. Đề cao việc trao đổi trực tiếp, giảm việc trao đổi gián tiếp hay hinh thức thông qua các văn bản. | The one or two iterations means that the programmers clearly need to know what stories are in the iteration they are currently working on. It s also useful to know what s in the next iteration. Beyond that the iteration allocation is not so useful. However the business needs to know what is currently in this release and it s useful to know what s in the release after that. The real decider for how long in advance you should plan is the cost of keeping the plan up to date versus the benefit you get when you know that plans are inherently unstable. You have to honestly assess the value compared to the volatility of the plans. How do you Keep the Release Plan Our preferred form of release plan is a set of cards. Each card represents a user story and contains the essential information to describe what the story is about. You group the cards together to show which stories are in this release. Lay out stories with adhesive on a wall or pin them up on a cork board. Wrap future stories with a rubber band and stick them safely in a drawer. We like cards because they are simple physical devices that encourage everyone to manipulate them. It s always that little bit harder for people for people to see and manipulate things that are stored in a computer. However if you want to store this in a computer go ahead. Just do it in a simple way preferably in a way that just a little too simple. A simple spreadsheet often does the job best. We ve often noticed that people who use complicated project management packages are prone to spending time fiddling with the package that they should be spending communicating with other people. How much can you put into a release If you have stories iterations and releases you need to know how many stories you can do in each iteration and release. We use the term velocity to represent how much effort there is available in a release. We estimate the velocity of the team and estimate the amount of effort required for each story see Chapter 19 for .
