Infrastructure Interdependencies: Modeling and Analysis

In this chapter some of the most well established approaches to model Critical Infrastructure Interdependencies are discussed. Specifically the holistic methods, where the interaction among infrastructures is seen from a very high level of abstraction, are compared with agent-based models, where the dependency phenomena that may arise among subsystems are considered both in terms of functional and topological relations. In order to better clarify the different approaches, the Input–Output Inoperability Model is discussed as one of the most representative Holistic methodologies; Agent-based methods are then discussed with particular reference to the Agent-Based Input–Output Inoperability Model, an extension of the Input–Output Inoperability Model, developed by the authors. The increased level of detail clashes with the lack of adequate quantitative data required to tune the models, which are typically assessed based on economic exchange among infrastructures; in order to partly overcome such an issue, an Input–Output methodology based on the theory of Fuzzy Systems is discussed. Finally, some conclusive remarks and open issues are collected.