Delaying difficult design decisions

The context of this paper is system engineering of the software needed in constructed complex systems, which are large systems managed or mediated by computing systems. In this paper, we describe an approach to systems engineering design and modeling that allows difficult design decisions to be delayed until enough information is available to make them properly. We use our Problem Solving Interpretation of programming languages to allow a mix of specification and implementation throughout the design process, and a model-based approach to design that provides an executable specification/model of the system at all stages of its development.