Assessing hybrid incremental processes for SISOS development

New processes are being assessed to address modern challenges for Software-Intensive Systems of Systems (SISOS), such as coping with rapid change while simultaneously assuring high dependability. A hybrid agile and plan-driven process based on the spiral lifecycle has been outlined to address these conflicting challenges with the need to rapidly field incremental capabilities in a value-based framework. A system dynamics model has been developed to assess the incremental hybrid process and support project decision-making. It estimates cost and schedule for multiple increments of a hybrid process that uses three specialized teams, and also considers the mission value of software capabilities. It considers changes due to external volatility and feedback from user-driven change requests, and dynamically re-estimates and allocates resources in response to the volatility. Deferral policies and team sizes can be experimented with, and it includes tradeoff functions between cost and the timing of changes within and across increments, length of deferral delays, and others. We illustrate how the model can be used to determine optimal agile team size to handle changes. Both the hybrid process and simulation model are being evolved on a very large scale incremental SISOS project and other potential pilots.