  A key challenge in System of Systems (SoS) engineering is the analysis and
maintenance of global properties under SoS evolution, and the integration of
new constituent elements. There is a need to model the constituent systems
composing a SoS in order to allow the analysis of emergent behaviours at the
SoS boundary. The Contract pattern allows the engineer to specify constrained
behaviours to which constituent systems are required to conform in order to be
a part of the SoS. However, the Contract pattern faces some limitations in
terms of its accessibility and suitability for verifying contract
compatibility. To address these deficiencies, we propose the enrichment of the
Contract pattern, which hitherto has been defined using SysML and the COMPASS
Modelling Language (CML), by utilising SysML and Object Constraint Language
(OCL). In addition, we examine the potential of interface automata, a notation
for improving loose coupling between interfaces of constituent systems defined
according to the contract, as a means of enabling the verification of contract
compatibility. The approach is demonstrated using a case study in audio/video
content streaming.
