# A Review of Supply Chain Resilience: A Network Modeling Perspective
## 2 Overview of Supply Chain Resilience Development
### Fundamental Concept of Resilience
#### 2.1.2 The Relationship Among Resilience, Flexibility, Robustness, Vulnerability, and Reliability  
Resilience, flexibility, robustness, vulnerability, and reliability are commonly used concepts in systems science and engineering. Each has distinct definitions and application contexts, addressing various system characteristics in response to external shocks, internal failures, or environmental changes. While these concepts describe different aspects of a \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Type** & **Equilibrium State** & **Research Focus** & **Connotation** & **Target System** \\ \hline Engineering & & & & The system adapts and recovers to its normal state after disturbances, emphasizing adaptability and recovery speed and extent. & Physical systems \\ Resilience & & & Maximum disturbance a system can withstand before changing its equilibrium state & equilibrium state to another after disturbances, emphasizing the stability of the system structure and function. & Ecological systems \\ Evolutionary Resilience & & & & Resilience is a continuously evolving process, with the potential to create new development pathways, emphasizing the adaptive transformation of the system structure and function. & Economic systems \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparison of resilience concepts. system's adaptability and recovery capacity from different perspectives, they also exhibit the following specific intrinsic interconnections [18]:  
1. Reliability refers to a system's ability to perform its specified functions under predetermined conditions within a specified time frame. A reliable system maintains regular operation during the expected period, with a low probability of failure;
2. Vulnerability describes the degree to which a system is susceptible to damage or functional failure when exposed to external or internal threats. A highly vulnerable system lacks resistance to disturbances or shocks and is prone to failure. High vulnerability indicates insufficient protective mechanisms or response strategies, making the system more susceptible to harm;
3. Robustness is the ability of a system to maintain its normal functions in the face of uncertainty, disturbances, or environmental changes. A highly robust system can withstand a certain degree of shocks or failures without losing functionality. Robustness is often associated with system stability and strength, emphasizing the capacity to operate continuously even when subjected to certain levels of disruption;
4. Flexibility refers to a system's ability to adapt to changes in the environment or demands. A highly flexible system can adjust to maintain functionality or improve efficiency amidst change. Flexibility does not necessarily imply maintaining original functionality after a shock but involves reconfiguring strategies, structures, or configurations to adapt to new conditions;
5. Resilience is the ability of a system to recover from disturbances, shocks, or failures and return to its original state or adapt to a new environment. Resilience emphasizes recovery capacity and adaptability. It relates to a system's self-repair and recovery mechanisms, particularly the ability to quickly return to normal or establish a new equilibrium after partial failures or disruptions [19; 20; 21]. The distinctions and similarities among resilience, flexibility, robustness, vulnerability, and reliability primarily manifest in the following aspects: Reliability pertains to the probability of regular operation, emphasizing the absence of system failures. Vulnerability reflects the weaknesses of a system under threats, indicating the degree to which the system is prone to damage. It is conceptually opposite to reliability, as high vulnerability often implies lower robustness, flexibility, and resilience. Robustness focuses on a system's ability to continue functioning under disturbances without requiring adjustments or adaptations. Systems with high robustness typically exhibit low vulnerability but may not possess flexibility or resilience.