  System-of-Systems (SoS) has consolidated itself as a special type of
software-intensive systems. As such, subtypes of SoS have also emerged, such as
Cyber-Physical SoS (CPSoS) that are formed essentially of cyber-physical
constituent systems and Systems-of-Information Systems (SoIS) that contain
information systems as their constituents. In contrast to CPSoS that have been
investigated and covered in the specialized literature, SoIS still lack
critical discussion about their fundamentals. The main contribution of this
paper is to present those fundamentals to set an understanding of SoIS. By
offering a discussion and examining literature cases, we draw an essential
settlement on SoIS definition, basics, and practical implications. The
discussion herein presented results from research conducted on SoIS over the
past years in interinstitutional and multinational research collaborations. The
knowledge gathered in this paper arises from several scientific discussion
meetings among the authors. As a result, we aim to contribute to the state of
the art of SoIS besides paving the research avenues for the forthcoming years.
