  Context: The systems comprising a system of systems (SoS) are inde- pendently
acquired, operated, and managed. Frequently, the architecture documentation of
these existing systems addresses only a stand-alone perspective, and must be
augmented to address concerns that arise in the integrated SoS. Objective: We
evaluated an architecture documentation viewpoint to address the concerns of a
SoS architect about a constituent system, to support SoS design and analysis
involving that constituent system. Method: We performed an expert review of
documentation produced by applying the viewpoint to a system, using the active
review method. Results: The expert panel was able to used a view constructed
using the baseline version of the viewpoint to answer questions related to all
SoS architect concerns about a constituent system, except for questions
concerning the interaction of the constituent system with the platform and
network infrastructure. Conclusions: We found that the expert panel was unable
to answer certain questions because the baseline version of the viewpoint had a
gap in coverage related to relationship of software units of execution (e.g.,
processes or services) to computers and networks. The viewpoint was revised to
add a Deployment Model to address these concerns, and is included in an
appendix.
