# Resilience in the Cyberworld: Definitions, Features and Models
## 4 Model of Key Actions  
The key actions of resilient systems were introduced in Section 2. In this section their dynamic relationships are shown and explained.  
The key actions are mentioned completely or partially in many publications, but [PERSON] in [6] establishes a direct connection between them in the form of a cycle as shown in Figure 2. [PERSON]'s paper is not about implementing an IT system, but about the ability of different departments, components and participants to respond when a disaster occurs. This responsiveness must be constantly improved in the sense of [PERSON]'s publication in order to keep (permanent) damage and loss of life as low as possible. The concept presented by [PERSON] is intended to implement a system-wide approach that will support the challenges of managing the United States' water resource infrastructure. However, this abstract concept can be transferred to IT systems.  
The cycle shown in Figure 2 is started when a disturbance occurs, and is considered successful once it has been completed for a disturbance. A learning effect is considered to have occurred when there is a measurable improvement if the same fault occurs again in the future.  
A disturbance is considered to be an adversity that has negative effects on the system. Negative effects are consequences that interfere with the intention of the system, i.e., in a certain way with its task. In the worst case, the compromised system can no longer fulfill its tasks. Disturbances can be caused by malicious, nonmalicious, anthropogenic (influenced or caused by humans), nonanthropogenic, internal and external influences.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Anticipation** & **Resistance** & **Recovery** & **Adaptation** & **Detection** \\ \hline Robustness & & **X** & **X** & & \\ Reliability & & **X** & **X** & & \\ Adaptability & & **X** & **X** & **X** & \\ Evolvability & & & & **X** & \\ Security & **X** & **X** & & & **X** \\ Safety & **X** & **X** & & & **X** \\ Assessability & & & & & **X** \\ Integrity & **X** & **X** & & & \\ \hline \hline \end{tabular}
\end{table}
Table 3: Mapping of the mentioned attributes to the key actions.  
The four key actions shown in Figure 2 and the resulting cycle are to be understood according to [PERSON] [6] as follows:  
1. **Prepare/Anticipate/Plan:** This key action includes a natural process, or under certain circumstances, an anthropogenic activity, with the aim of preparing the system for a disturbance.
2. **Resist/Absorb/Withstand:** This is the ability to withstand a disturbance while maintaining a certain level of functionality.
3. **Recover/Bounce Back:** The lost functionality must be restored. If it is not possible to maintain functionality, the system shall be able to return to its original state.
4. **Adapt/Transform/Bounce Forward:** This ability to adapt involves putting a system into a state that is better able to withstand or recover from disruption. Ideally, this adaptation leads to reduced loss of functionality and a shorter recovery time. Figure 3 shows the process of increasing resilience schematically. However, the process of adaptation only occurs when the cycle has been completed and applies only to this type of disturbance.  
Figure 3: Schematic representation of the learning effect. A system is influenced by a disturbance and loses functionality. This loss must be resisted. Through the process of restoration and adaptation, a similar disruption will trigger a less severe loss of functionality in the future and the time to restore the system is shortened (image based on: [6]).  
Figure 2: Presentation of key actions in a cycle (image based on [6]).  
In [PERSON] [8], the principle of key actions was extended to include the ability to detect a threat. According to [PERSON] [8], a system must first be able to detect a threat in order to respond appropriately to it in the next step. Figure 4 shows the cyber-resilience lifecycle according to [PERSON].