## 5 Case Study
### Target System for Structured Feature Analysis  
The target system for the application of structured features was a vehicle door control system that included functional requirements such as checking whether the vehicle doors were locked or unlocked. To demonstrate the traceability of functional requirements and hardware elements to component architecture elements within SFCAD, we present the software functional requirements necessary for system development along with the hardware system model that influences the software development process. For this case study, 15 functional requirements were selected from among 31, focusing on those related to the hardware elements identified in the system specifications as well as those impacted by the hardware system.  
Figure 7 shows a subset of the functional requirements related to the knob switch. The functional requirements are described alongside the hardware system necessary for the proper operation of the requirements, differentiating between the two. Among these, hardware elements that were ambiguous or unrelated to the selected functional requirements were excluded from the hardware system model and elements related to security were partially renamed.  
Based on the overall system requirements specification, we analyzed the relationships between the hardware elements associated with the software functional requirements and derived the hardware system model by applying the sensor-actuator pattern, as shown in Figure 8. Centered around the Integrated Control Unit (ICU), the hardware system model consists of an H/W switch section, Controller Area Network (CAN), and H/W actuator section. In the hardware system model, the hardware switch section represents the components that send signals to the ICU, which is equipped with software, the CAN section serves as the communication channel that receives the data processed by the ICU, and the hardware actuator section represents the components that control the external environment. These elements are interconnected to control the system. The hardware system model is composed of hardware switch sensors, actuators, and network communication-related elements, making it a suitable example for illustrating the structure of software embedded in vehicles.  
Using the provided requirements and hardware system model, we conducted a structured feature analysis and generated a structured feature list. The structured feature list from the case study consisted of 106 structured features, a subset of which is shown in Figure 9. As in Figure 2, each attribute of the structured feature is represented by a column in the structured feature list. In Figure 6, the software functional requirements are linked to RID and the hardware system elements are connected to ID, OD, IE, and OE, indicating that the analysis has been conducted.  
Figure 8: Hardware system model.  
Figure 7: Functional requirements.  
In this case study, the application of structured features assumes that the structured feature analysis has already been completed and that a structured feature list has been generated. Thus, the pairs \(SF_{id\_RID}\), \(SF_{id}\), that is, REQ_F_01-01, SF-001 and REQ_F_01-01, SF-002 in Figure 9, have already been derived. Therefore, the information for mapping requirements and structured features is already available in the structured feature list, which is used to create the traceability matrix.