The pervasiveness of the communication networks increasingly has made possible to interconnect software‐intensive systems that were independently developed, operated, managed, and evolved, yielding a new kind of complex system, that is, a system that is itself composed of systems, the so‐called System‐of‐Systems (SoS). Nowadays, the Internet‐of‐Things (IoT) enables the engineering of software‐intensive SoS, which are opportunistically constructed for achieving specified missions in specific operational environments. In particular, in the subset of IoT where “things” are predominantly connected vehicles, the so‐called Internet‐of‐Vehicles (IoV), the challenge is to exogenously coordinate different vehicles for performing together, through emergent behavior, traffic‐related missions, especially platooning. In platooning, two or more vehicles are connected together in convoy using wireless connectivity and automated driving support. The corresponding challenge in the architectural design of SoSs on IoV is to conceive concepts and mechanisms for describing how an SoS architecture is able to create, on the fly, and maintain emergent behaviors from elementary connected vehicles, where the actual vehicles are not known at design time. To address this challenge, this paper investigates the principle of supervenience for describing architecture‐driven emergent behavior following an exogenous approach. In particular, it describes the concepts and mechanisms underlying SosADL, a formal SoS Architecture Description Language (ADL), based on the novel π‐Calculus for SoS, to support the architectural description of self‐organizing SoSs, upwardly causing the required SoS emergent behaviors at run time. Especially, it demonstrates how architectural mediators expressed with SosADL in exogenous SoS architectures support vehicle platooning through an excerpt of a real application on the IoV.