## 2 Problem Formulation
### Access Control Framework for Multilayered Railway Systems  
Since the concept of an access control matrix was proposed, many access control models have emerged, such as discretionary access control (DAC), mandatory access control (MAC), usage control (UCON), task-based access control (TBAC), role-based access control (RBAC), and attribute-based access control (ABAC). They each have their own characteristics and have been widely used in different environments. DAC excels in its flexibility in authorization. MAC demonstrates outstanding performance in system security \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Data Item**} & \multicolumn{4}{c}{**Category**} & \multirow{2}{*}{**Hierarchy**} & \multirow{2}{*}{**Timeliness**} \\  & **1 st-Level Subclass** & & & & \\  & **of Business** & & & & \\ \hline Bridge location & Management & Construction & Bridge construction & 2 & Static \\ \hline Tunnel length & Management & Construction & Tunnel construction & 2 & Static \\ \hline Slope rate & Management & Construction & Roadbed construction & 2 & Static \\ \hline Locomotive inspection and repair & Management & Equipment & Locomotive and vehicle & 4 & periodical \\ \hline Operating status of computer-interlocking system & Management & Monitoring & Fixed facility monitoring & 3 & Real-time \\ \hline Train operation safety monitoring information & Management & Monitoring & Mobile facility monitoring & 3 & Real-time \\ \hline Slope displacement monitoring & Management & Monitoring & Disaster monitoring & 3 & Real-time \\ \hline Train electricity consumption & Production & Train & Electric information & 2 & Periodical \\ \hline Balise inspection/service logs & Production & Operation and maintenance & Facilities maintenance & 3 & Periodical \\ \hline Statistics of ticket reservation & Production & Dispatch & Passenger flow forecast & 1 & Real-time \\ \hline Freight train formation plan & Production & Dispatch & Train operation plan & 4 & Real-time \\ \hline Train speed and position measurement & Production & Train control & Operational control & 4 & Real-time \\ \hline Passenger ID information & External & User & Passenger & 4 & Periodical \\ \hline Organization code & External & User & Supplier & 2 & Periodical \\ \hline Passenger throughput & External & Network & Network traffic & 2 & Periodical \\ \hline Passenger arrivals & External & Passenger flow & Transfer station & 4 & Periodical \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Typical categorization and hierarchization of rail transit data. and confidentiality. RBAC has advantages in terms of intuitive understanding, flexible authorization, separation of duties, and descriptive capabilities. ABAC performs well in descriptive capabilities and access control granularity. To select a suitable access control framework for the data interaction scenarios in rail transit, we need to quantitatively compare the performance of these widely used models. So far, there is no unified quantitative evaluation standard in the industry to measure the effectiveness and quality of access control models. In this paper, we mainly consider the basic capabilities from four aspects: control capability, operating cost, coverage, and usability. Specifically, we used a set of indicators to measure the performance of access control models, namely criteria = {granularity, expressiveness, complexity, scalability, compatibility, flexibility, security}, where granularity and expressiveness are suitable criteria to measure the control capability, complexity shows the operating cost, scalability, and complexity reflecting the coverage, while flexibility and security refer to the usability. As for the application scenarios of the multilayer domain rail transit system, the security is the most significant since some data concerns national and public safety, and the control capability and coverage come posteriorly to achieve universal access control. Therefore, the corresponding weights were set as \(w\) = {0.2, 0.1, 0.05, 0.1, 0.2, 0.1, 0.25}.