  Multi-scale structures are prevalent in both natural and artificial systems,
as they can handle increasing complexity. Several terms are employed almost
interchangeably across various application domains to refer to the multi-scale
concept - e.g., hierarchy, holarchy, multi-level, multi-layer, nested,
embedded, micro-macro or coarse graining. While the concrete meanings behind
these terms may differ slightly, several core commonalities persist across all
cases. In this position paper we aim to highlight these common features of the
multi-scale concept, as a preliminary basis for a generic theory of multi-scale
systems. We discuss the concepts of scale and multi-scale systems in general,
and then of multi-scale feedback systems in particular, focusing on the role
played by information in such systems. Our long-term objective is to develop a
general theory of multi-scale feedback systems, applicable across all domains
dealing with complex systems.
