Abstract
Software development project managers have already known that adding manpower to a late software project makes it later. This is a famous sentence in "Mythical man-month" written by Brooks. The managers also recognize that even if two man-month workloads are assigned to two developers, the development period is not one month. However, the managers want to see when the two developers finish the two man-months workload. Of course, the managers don't think that the development period reduces from two months to one month. If the development period in the two developers is shorter than two months, the managers will decide to add the new developer to the work. Therefore, we propose a new workload estimation model based on communications among shared works. The model includes Concept Model of UML of a software development project. The classes and relationships in the Concept Model present the kinds of works and relationships among the works, respectively. Sharing works causes increments of communication workload. The communication workload is derived from the relationships among the classes in the Concept Model. In case studies using the model, we were able to reconfirm quantitatively the famous sentence of "Mythical man-month".