Systems-of-systems (SoS) are network-enabled synergistic collaborations between systems that are operationally and managerially independent, distributed, evolve dynamically and exhibit emergence. The design of dependable SoS requires model-based approaches that permit description of contracts between constituent systems at interfaces in a SoS architecture, including functionality and interaction behaviour, and that permit verification of global behaviours. We describe an approach to formal model-based SoS engineering using complementary notations for functional, interaction and architectural aspects. A case study in modelling information flow in an emergency response SoS demonstrates the viability of the proposed approach and highlights a need for common semantic foundations.