  Different graph generalizations have been recently used in an ad-hoc manner
to represent multilayer networks, i.e. systems formed by distinct layers where
each layer can be seen as a network. Similar constructions have also been used
to represent time-varying networks. We introduce the concept of MultiAspect
Graph (MAG) as a graph generalization that we prove to be isomorphic to a
directed graph, and also capable of representing all previous generalizations.
In our proposal, the set of vertices, layers, time instants, or any other
independent features are considered as an aspect of the MAG. For instance, a
MAG is able to represent multilayer or time-varying networks, while both
concepts can also be combined to represent a multilayer time-varying network
and even other higher-order networks. Since the MAG structure admits an
arbitrary (finite) number of aspects, it hence introduces a powerful modelling
abstraction for networked complex systems. This paper formalizes the concept of
MAG and derives theoretical results useful in the analysis of complex networked
systems modelled using the proposed MAG abstraction. We also present an
overview of the MAG applicability.
