Systems-of-systems are characterized by the independence of their constituent elements. Those elements are usually socio-technical, comprising technology, humans, and organizations. To capture their independence, they need to be viewed as intelligent agents that rely on internal models of the world for their decision-making. Hence, a system-of-systems model will include agents that inside themselves contain other models of the same system-of-systems. Describing these overlapping subjective models and their usage by the agents is essential to properly understand the resulting behavior of the overall system-of-systems. Current modeling practices are not well suited for dealing with this, and the paper therefore outlines an ontology that makes the agents and their internal models more explicit. The paper also discusses the implications such models have on sys-tems engineering practices and how they address known system-of-systems engineering pain points.