Requirements are the New Code

Unforeseen safety and security failures in complex software-intensive systems arise due to hidden dependencies between system components and artifacts. These stem from stakeholder misunderstanding of system artifact and component interactions. In most systems, artifacts are defined and described, and components are designed, implemented, and combined by engineers in multiple disciplines. Also, artifacts are described in places separated by hundreds of pages or files and in different domain and description languages, including natural, graphical, and domain-specific languages. Hence, it is of primary importance, but also currently extremely difficult, to discover these hidden dependencies. To help engineers find these dependencies, and hence better foresee erroneous interactions, an approach that enables and promotes a holistic, hierarchical, and incremental description of a system is needed. In this article, we introduce EXMPLRAD. EXMPLRAD is a human-centered language that enables the description and integration of informal and formal requirements, architectural and design descriptions, source code, and configuration artifacts, and their relationships in a format that resembles code. A holistic system model described using EXMPLRAD enables the creation and application of methods for the automatic discovery of hidden dependencies. We demonstrate this with a case study that analyzes the seL4 microkernel's Inter- Process Communication subsystem including the modeling of its requirements, architecture, and source code in C.