  The cutting edge in systems development today is in the area of "systems of
systems" (SoS) large networks of inter-related systems that are developed and
managed separately, but that also perform collective activities. Such large
systems typically involve constituent systems operating with different life
cycles, often with uncoordinated evolution. The result is an ever-changing SoS
in which adaptation and evolution replace the older engineering paradigm of
"development". This short paper presents key thoughts about verification and
validation in this environment. Classic verification and validation methods
rely on having (a) a basis of proof, in requirements and in operational
scenarios, and (b) a known system configuration to be proven. However, with
constant SoS evolution, management of both requirements and system
configurations are problematic. Often, it is impossible to maintain a valid set
of requirements for the SoS due to the ongoing changes in the constituent
systems. Frequently, it is even difficult to maintain a vision of the SoS
operational use as users find new ways to adapt the SoS. These features of the
SoS result in significant challenges for system proof. In addition to
discussing the issues, the paper also indicates some of the solutions that are
currently used to prove the SoS.
