A requirements monitoring model for systems of systems

Many software systems today can be characterized as systems of systems (SoS) comprising interrelated and heterogeneous systems developed by diverse teams over many years. Due to their scale, complexity, and heterogeneity engineers face significant challenges when determining the compliance of SoS with their requirements. Requirements monitoring approaches are a viable solution for checking system properties at runtime. However, existing approaches do not adequately consider the characteristics of SoS: different types of requirements exist at different levels and across different systems; requirements are maintained by different stakeholders; and systems are implemented using diverse technologies. This paper describes a three-dimensional requirements monitoring model (RMM) for SoS providing the following contributions: (i) our approach allows modeling the monitoring scopes of requirements with respect to the SoS architecture; (ii) it employs event models to abstract from different technologies and systems to be monitored; and (iii) it supports instantiating the RMM at runtime depending on the actual SoS configuration. To evaluate the feasibility of our approach we created a RMM for a real-world SoS from the automation software domain. We evaluated the model by instantiating it using an existing monitoring framework and a simulator running parts of this SoS. The results indicate that the model is sufficiently expressive to support monitoring SoS requirements of a directed SoS. It further facilitates diagnosis by discovering violations of requirements across different levels and systems in realistic monitoring scenarios.