## 5 System Development and Design
### The SRs Knowledge Graph Requirement Representation Module  
The SRs representation knowledge graph construction module is the core component of the entire prototype model. Based on the principles of domain knowledge graph construction proposed in Section 3.4, the structured requirement data are utilized to extract node attributes (subject, attribute, object), edge attributes (action), and textual elements (function, value, principle, condition) to establish the requirement representation graph. Using physical requirements as the foundational framework for the domain requirement representation knowledge graph, its specific function is shown in Figure 9. Taking a partial magnified view of the \"Automatic Fare Collection System\" node as an example, this system is composed of several subsystems, including \"Station Computer System, Central Clearing System, Training System, Transmission Channel, Maintenance and Testing System, Tickets\", etc. Each subsystem contains the corresponding constituent elements that it should possess. Using this graph framework, the knowledge structure based on physical requirements is clearly presented, encompassing the core nodes and elements of the entire metro system. Based on this framework, the remaining four types of requirements (functional requirements, interface requirements, performance requirements, and design constraints) are gradually added to the requirement graph, thereby forming a complete system requirement representation. The SR representation knowledge graph for Chapters 18-22 of the 'Code for Design of Metro' is shown in Figure 10. When hovering over the node \"Automatic Fare Collection System\", the functionalities that this node should possess will be displayed, such as processing urban-integrated circuit card tickets, having user permission management capabilities, and providing clear information prompts, among others. All nodes with functional requirements will have the prefix \"F\" added to their names to indicate that the node contains functional requirements, making it easier for users to understand the functionalities it should possess. Design constraints will add specific limitations to the attributes associated with the nodes, and these design constraints are displayed in purple ellipses. When hovering over a node or connecting edge, the specific constraints of the corresponding attribute will be shown. For example, when hovering over the connecting edge between the \"Automatic Fare Collection System\" and \"Management Mode\"  
Figure 9: (**a**) Knowledge graph framework based on physical requirements, (**b**) physical relationship graph of the node “Automatic Fare Collection System”. nodes, the requirement that the system must adopt a \"three-level management model of station, line ticketing center, and network ticketing center\" will appear. Performance requirements are indicated by green triangles on the attribute nodes. When hovering over an attribute node or its connecting edge, the specific requirements for that attribute from the subject will be displayed. For example, the \"Design Capacity\" attribute of the \"Automatic Fare Collection System\" requires \"meeting the requirements for metro peak passenger flow\". Interface requirements reflect the interconnection between subjects and associated objects, represented by orange pentagrams on the attribute nodes of the associated objects. When hovering over the connecting edge between the subject and the associated object, the system will display the specific requirements for the interface interaction between the subject and the object. For example, the connection between the \"Automatic Fare Collection System\" and the associated object \"Clock\" requires that the \"Automatic Fare Collection System\" provides \"Interface Technical Requirements\" to the \"Clock\". The SRs knowledge graph requirement representation module construction logic is integrated into the system, as shown in Figure 11. The SRs knowledge graph requirement representation module contains multiple functional areas.