During the development of the project, the user will ask for new requirements at any time, and ask the developers to solve them. These requirements are sometimes raised in the development phase and sometimes after the development phase. In the two adjacent sub-phases of the demand analysis, or in the demand analysis of the iteration cycle, the demand analysis results of the latter paragraph or period are inconsistent with the previous one. We call this inconsistency a demand change. There are several reasons for the change in demand:

(1) In the demand analysis phase, the communication between the developer and the user is insufficient. In the demand analysis phase, the developer and the user do not have good communication, and the developer will derive the user's needs according to the general information provided by the user. The demand drawn from this demand analysis tends to be far from the actual needs of the user, causing users to propose changes.

(2) The implementation cycle of the project is too long. Over time, users have become more aware of the entire system. They put more and more requirements on the interface, function and performance of the module.

(3) Technology update is too fast. Due to the rapid update of technology, enterprises may introduce new devices that may have a direct relationship with our target system. Since this change may occur before or during the resolution of the user's original problem, the developer may not Do not join this new demand.