  The critical infrastructures of the nation such as the power grid and the
communication network are highly interdependent. Also, it has been observed
that there exists complex interdependent relationships between individual
entities of the power grid and the communication network that further
obfuscates the analysis, and mitigation of faults in such multi-layered
networks. In recent years, the research community has made significant efforts
towards gaining insight and understanding of the interdependency relations in
such multi-layered networks, and accordingly, a number of models have been
proposed and analyzed towards realizing this goal. In this chapter we study
existing interdependency models proposed in the recent literature and discuss
their approach, and inherent features, towards modeling interdependent
multi-layer networks. We also provide a brief discussion into the drawbacks of
each of these models and propose an alternate model that addresses these
drawbacks by capturing the interdependency relationships using a combination of
conjunctive and disjunctive relations.
