A Framework for System Resilience Discussions

This paper presents a framework for discussions of system resilience. The framework has five aspects: time periods, system types, events, resilience actions, and properties to preserve. The five time periods are well defined, but the other four aspects vary according to author, type of system, and purpose of the discussion, so what is presented is the variation that occurs among definitions. The framework is followed by a cataloging of principles for creating emergence, including a number of rubrics. Finally the paper discusses factors affecting resilience, including improving resilience, tradeoffs, and loss of resilience. An appendix details specific definitions and distinguishers from related properties. Introduction and organization A key challenge for systems of the present and the future is to build in resilience, so that the systems can withstand unpredicted or even predicted adverse events. Resilience has many definitions, some of which include requirements on the recovery of the system and for the safety of the humans within the sphere of the influence of the system. This paper considers the phenomenon of resilience to subsume robustness, survivability, safety, some parts of security, and some aspects of other system characteristics such as reliability. Engineering for resilience looks at a cycle in time of potential events and at the steps needed prior to, during, and following an event. This white paper surveys the resilience literature in order to understand what aspects are important, which aspects are in agreement, and which aspects are in controversy. The objective is a framework that can be used to bring together knowledge about building resilience into systems and enterprises. This paper first describes a framework of resilience attributes. These include time periods, types of systems, types of events, required system actions, and qualities that must be preserved for the system to be considered resilient. The second section collects principles on how to build resilience into systems. This section provides first sets of heuristics or principles and then rubrics, sometimes considered methodologies, for building in resilience. Notes follow on what strategies might improve resilience, involve tradeoffs, or make resilience more difficult. An appendix is included which defines resilience in two ways: explicitly, by quoting or paraphrasing definitions from the literature, and then implicitly, by contrasting resilience with other qualities. 1 Other taxonomies exist; [Alberts and Hayes 2003], for example, considers robustness and resilience to be two of the six constituents of agility, the others being responsiveness, flexibility, innovation, and adaptation.