# Resilience in the Cyberworld: Definitions, Features and Models
## 2 Definitions
This means that its specific and distinctive functional and non-functional features should not be affected. Ref. [6] deals with the management of water resources, and was written from the perspective of the USACE (US Army Corps of Engineers). According to [PERSON] [6], resilience is a cycle consisting of anticipation, resistance, recovery and adaptation. Anticipation is the starting point of the cycle, while adaptation marks the end. The cycle is started by the occurrence of an event that affects the system in some way. This event is called a disruption. Specifically, [PERSON] defines resilience (in this case coastal resilience) as follows:  
_\"(Coastal) resilience is defined as the ability of a system to prepare, resist, recover, and adapt to disturbances in order to achieve successful functioning through time\"._  
A disturbance occurs here as an effect of a hazard on the infrastructure, system, etc. A hazard is an environmental or adverse anthropogenic condition. The article by [PERSON] published in 2016 [25] defines the ability of a system to reduce the extent and the duration of disruptions as resilience. Disruptive events are not always predictable, but when they occur they are supposed to lead to a learning and adaptation effect of the system. Adaptation is crucial when it comes to realizing resilience against cyberaccidents, since the cyberlandscape is developing very rapidly. [PERSON] says in his article that errors must be detected and understood. It must be possible for the system to adapt to the errors or the error situation and a fast recovery must be guaranteed. The system must recover quickly after the occurrence of an error. If this is not possible, the error and the resulting faulty system environment must be dealt with appropriately. The U.S. National Institute of Standards and Technology (NIST) [7] coins the term cyber-resilience to clearly distinguish its approach from the general definitions of resilience. Cyber-resilience is the following property:  
_\"Cyber Resilience is defined in this publication as the ability to anticipate, withstand, recover from, and adapt to adverse conditions, stresses, attacks, or compromises on systems that include cyber resources\"._  
According to NIST, the definition of cyber-resilience refers specifically to all entities that contain cyber-resources. A cyber-resource is an information resource that creates, stores, processes, manages, transmits, or disposes information in electronic form and that can be accessed over a network or by network methods. The definition of NIST can therefore be applied to a system, a mechanism, a component or a system element, a common service, an infrastructure or a system of systems, etc. Publications [8] and [9] do not present completely new definitions for cyber-resilience. These publications refer to already-known sources such as NIST [7] for a definition. Publication [8] by [PERSON] extends the previously mentioned circuit ([PERSON] [6]) to include the ability of a system to detect threats. [PERSON] calls this new cycle the cyber-resilience life cycle. This approach is described in detail in Section 4. Publication [9] by [PERSON] considers cyber-resilience as an effective countermeasure against cyberattacks or cyberthreats. In [45], the link between security and cyber-resilience is also discussed. The publications selected here show that the type and scope of the definitions of resilience depend very much on the respective (informatics) application area. However, some key actions can be filtered out, which appear at least partially in all the publications considered here: Anticipating, resisting, recovering, detecting and adapting (to threats of any kind). In some publications, such as [6; 7; 46] these key actions are even mentioned explicitly. Thus, we filtered these five key actions out of the definitions. Table 2 shows which key action is mentioned in which of the publications considered here.