Discussing resilience in the context of cyber physical systems

Cyber-Physical Systems (CPSs) are increasingly more complex and integrated into our everyday lives forming the basis of smart infrastructures, products, and services. Consequently, there is a greater need for their ability to perform their required functions under expected and unexpected adverse events. Moreover, the multitude of threats and their rapid evolution pushes the development of approaches that go beyond pure technical reliability, rather encompassing multi-dimensional performance of a socio-technical system. These dimensions call for the notion of resilience, to be used as a staging area for modelling system performance. While a large number of documents deal with this kind of problem for systems including CPSs, a comprehensive review on the topic is still lacking. The scope of this paper is to survey available literature for understanding to which extent CPSs contribute to system resilience, and to synthetize the approaches developed in this domain. More than 500 documents were reviewed through a protocol based on the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) review technique. This survey identifies main models and methods categorizing them on the basis of the hazards of interest and their effects on security, privacy, safety and business continuity. It also summarizes main conceptual frameworks and metrics used to assess and compare the resilience capabilities of a system including also CPSs. This cross-domain survey highlights the dominant techno-centric unit of analysis for available literature, still highlighting emerging trends towards more systemic representations of system threats, even socio-technically oriented, and respective modern investigation approaches.