Modeling and Analyzing Incremental Natures of Developing Software.

The basic premise of iterative and evolutionary project management is that a project is divided into early, frequent, and short duration delivery steps. Each step attempts to deliver some real value to stakeholders. The increment size and iteration length usually depend on profitability, finance, deadline, and so on, rather than the functionality of a developing system. It is difficult to guarantee the correctness in every iteration step. In this article, we propose a method of ensuring the correctness of iterative design in terms of deadlock-freedom of the behavior of software. The method first obtains the correct (deadlock-free) atomic subsystems of a system using a decomposition approach. In the iterative development process, the method then requires that one atomic subsystem or the composition of multiple atomic subsystems should be regarded as one increment. Every increment is naturally correct and can be completely independently developed, independently deployed, and independently maintained. The currently released system in each iteration step is naturally guaranteed to be correct. It is not necessary for developers to consider the composition of the increment and the previously released system may cause flaws and errors. We also discuss the approach for ensuring correctness when design modifications are made in an iteration step. Finally, we explore the automatic decomposition of a system into multiple atomic subsystems and present the corresponding algorithm. A case demonstrates these results.