7.1.2 The Systems Engineering Sandwich: combining requirements, models and design

Abstract

AbstractAs Systems Engineering problems and solutions become more complex, it is harder for engineers to describe them and harder for reviewers and other stake‐holders to understand the descriptions. What is needed is a more powerful way of describing both problems and solutions, which combines the textual approach with the diverse world of modeling, including the use of visual representation. The result would be more accurate and complete system descriptions that are easier to understand and communicate for all stakeholders involved.In the Systems Engineering “sandwich”, requirements management is the “bread and butter” of the development cycle, and system modeling provides the “filling“. The role of the filling provided by modeling is to hold the requirements layers together, and provide richer rationale for relationships between those layers.In our opinion, the key to integrating requirements management with system model is the recording of design rational in an organized way. Such rationale explains why requirements have been decomposed in particular ways, and how one layer of requirements is intended to satisfy the layer above. The focus for such information is the “design document“.The following benefits are identified as accruing from an effective process integration of requirements management and system modeling: System modeling adds formality to the design process that lies between each layer of requirements. System modeling supports the construction of a consistent vocabulary for the textual expression of requirements. The design rationale gathered around the system model becomes the rationale for tracing between layers of requirements. The structure of the system model can be used to give structure to the requirements document. System models can be embedded in system design documents. These can provide textual context for the system model, giving rationale for design choices, explanations of diagrams, etc. Impact analysis can be carried out uniformly through requirements and models. Non‐functional and performance requirements not captured in the model can be managed as textual statements.