Page 23 - Read Online

Page 124 of 139 Clédel et al. J Surveill Secur Saf 2020;1:119­39 I http://dx.doi.org/10.20517/jsss.2020.08

Table 1. Table of resilience definitions
Definition orientation
Reference Events System Service Resilience Goal
handling stability delivery capacities
Ayyub [27] ✓ Preparation, adaption, resistance, recovery
Dinh et al. [29] ✓ Fast post-event recovery
Haimes [28] ✓ Acceptable degradation, time, and costs
Vugrinet al. [26] ✓ Reduction of the performance level deviation
Werner [13] ✓ Psychological and social adaptation
Hollnagel [3] ✓ Recover from disturbances at an early stage
Hale and Heijer [30] ✓ Managing activities, anticipation of threats
Leveson et al. [31] ✓ Prevent/adapt to maintain a system property
Sundström and Hollnagel [32] ✓ Ability to adjust in a long time period
Wreathall [18] ✓ Continuity of operations during/after a mishap
Mauthe et al. [2] ✓ Same level of functionality in case of changes
McDonald [17] ✓ Stability and integrity of core processes
Rieger [16] ✓ State awareness and operational normalcy
Wreathall [18] ✓ Keeping or quick recovery of a stable state
Arghandeh et al. [25] ✓ Continuity of electricity flow
Clark and Zonouz [24] ✓ Service delivery and guarantee of recovery
Sterbenz et al. [21] ✓ Maintenance of an acceptable level of service
Thompson et al. [33] ✓ Maintenance of security state
Francis and Bekera [15] ✓ ✓ Continuity of normal service function
Holling [11] ✓ Population survival
Wei and Ji [34] ✓ Incidents handling

mal amplitude of disruptions that can be tolerated. To buffering capacities, Woods specified a need for margin
and tolerance assessments that determine how closely and how well a system is currently running near to its
performance boundaries.

Moreover, resilience is not directly associated with a capacity to absorb and mitigate incidents [22,36] . However,
a need for diversity is specified as it prevent vulnerabilities to become a single point of failure. This diversity
manages the vulnerabilities of components to incidents by the use of different components and processes for
similar functions, but it should also consider the exposition of components and processes to these incidents
with geographic or topological dispersion for example. Dinh et al. [29] decomposed absorbability into two
complementary properties. The first property is flexibility and can be considered as a synonym of stability in
the cited article, as it consists in maintaining the system production variation into a desired range while inputs
are changing slightly. The second property is controllability and indicates how easily a system can be brought
in a desired state.

3.2. Adaptability
Adaptability [26] ,alsoknownasflexibility [35] ,is“thedegreetowhichthesystemiscapableofself-reorganization
for recovery of system performance” and is described as “the ability to replace component or input with an-
other” or the “system’s ability to restructure itself” to face changes and external pressures. While this descrip-
tion could be associated with diversity, which is more commonly interpreted as part of absorbability, adapt-
ability is also concerned with changing the system structure, policies, and priorities to mitigate the impact of
a disruption.

Some works refer to adaptability as evolvability [22,36] . It represents the ability of a system to “accommodate
changes” by upgrading itself with new functions or technologies during design and implementation phases or
by dynamically adjusting its behavior or its architecture to face operational faults and attacks. Moreover, in [30] ,
the authors affirmed that resilience has to be continuously kept up-to-date as it can disappear or be ineffective
against specific threats.

One possible adaptive mechanism is the use of safe mode controls. It consists in using simple but extremely
reliable systems that prevent critical failures [20] . Safe mode depends on few input sources such as Earth’s