Research And Application Of Early Software Sizing Estimation

In the early stage of software life-cycle, due to planning project resources reasonably by developer, need to estimate the software size. In the project-review phase, need a quicker and more effective estimate method for obtaining software size to determine the budgets. This paper put forward early estimate method and E&Q estimate method suited for project-review.The present mainstream of software sizing method is functional point method. Constrained by imperfect requirement documents, high uncertainty and limited time, standard functional point method is not suitable for estimation in the early stage of software life-cycle. Need an early FP estimate method and choose proper one on account of different types of project.Project-review is an important phase in the early stage of software life-cycle in which reviewing time is usually constrained especially of large software project. Standard early estimate method consumes such long time that cannot satisfy practical demand. Need to study a quicker early estimate method.We have done some actual work on early software estimation and quick estimate method.1. We have studied applicability of main early FP estimate methods, finding that various methods are suitable for various software domains. MIS system applies COSMIC early estimate method and NESMA early estimate method. Real-time system applies COSMIC early estimate method. E&Q estimate method combined with COSMIC and IFPUG estimate method are applied by both MIS system and Real-time system. The simplified NESMA estimate method is proved to be more suitable for WEB system.2. We have validated validity of several early estimate methods. Validated the early estimate methods by three MIS system and two Real-time system , comparing the size deriving from early estimate methods to which from standard estimate method. Estimation of early estimate methods drift about 5% to 43% from the standard or actual value , while the savings in time (and costs) can be between 30% and 60%.3. According to the constrained time and high quality of project-review, we have proposed early estimate method based on expert experience and sampling. Decompose the software to modules, developers pre-estimate their size and cost and then declare funds. Estimator classifies software modules with expert experience based on the decomposition and details of requirement documents, measures the random sample of modules carefully, and estimates overall size of software project by quick and approximate estimate method.4. We have tried out E&Q estimate method based on expert experience and sampling which was proved to be applicable. Applied the method to a large software system project-review which involved 21 pieces of software, 390 modules and 21 development organizations and related to business system, real-time system and those two combined. If the method was applied in project-review, we can not only derive software size quickly and accurately, but also give a proof for the agreement of both sides. The actual estimate time is greatly reduced, and both sides acknowledge the result highly.