On the Constituent Attributes of Software and Organisational Resilience

Our societies are increasingly dependent on services supplied by computers & their software. New technology only exacerbates this dependence by increasing the number, performance, and degree of autonomy and inter-connectivity of software-empowered computers and cyber-physical "things", which translates into unprecedented scenarios of interdependence. As a consequence, guaranteeing the persistence-of-identity of individual & collective software systems and software-backed organisations becomes an important prerequisite toward sustaining the safety, security, & quality of the computer services supporting human societies. Resilience is the term used to refer to the ability of a system to retain its functional and non-functional identity. In this article we conjecture that a better understanding of resilience may be reached by decomposing it into ancillary constituent properties, the same way as a better insight in system dependability was obtained by breaking it down into sub-properties. 3 of the main sub-properties of resilience proposed here refer respectively to the ability to perceive environmental changes; understand the implications introduced by those changes; and plan & enact adjustments intended to improve the system-environment fit. A fourth property characterises the way the above abilities manifest themselves in computer systems. The 4 properties are then analyzed in 3 families of case studies, each consisting of 3 software systems that embed different resilience methods. Our major conclusion is that reasoning in terms of resilience sub-properties may help revealing the characteristics and limitations of classic methods and tools meant to achieve system and organisational resilience. We conclude by suggesting that our method may prelude to meta-resilient systems -- systems, that is, able to adjust optimally their own resilience with respect to changing environmental conditions.