## 5 Results and Discussion
### Nonfunctional Requirements  
Nonfunctional requirements do not address functionality but refer to system operation specifications and capabilities, i.e., environmental requirements [42]. * Mobility and decentralized storage  
Mobile health is a rapidly growing field and an essential requirement in healthcare application domains. As patients become more mobile these days, they desire the same portability for their health records [59; 60]. Another requirement is that decentralized storage can facilitate faster access to medical data in a protected manner [61] since there is no single point of failure, and it splits the records storage from a single server into multiple distributed nodes in the network. In addition, the storage of large files, such as X-rays, will impact the network's performance. * Performance, scalability, and availability  
Performance evaluation plays an essential role in the area of blockchain research, in particular PHRs; thus, it is critical to assure usability in practice [62]. New solutions should be assessed in a meaningful way to illustrate their efficiency and effectiveness, as well as the performance benefits and drawbacks of the new release [54]. \"The application's performance must be guaranteed for all transactions carried out to be attractive for the user groups\" [41]. In addition, the PHR should be consistent and available to deliver timely support and treatment options to the patients [63; 64]. * Security and privacy  
Currently, security and privacy among healthcare organizations remain challenges [65]. Data leaks and the distribution of patient medical records can have serious consequences, such as risks to patients' privacy through the selling of the data on the black market and malicious attacks that can harm a patient's reputation and finances [60]. Thus, the system should be secure and traceable. In addition, a one-time password is required when the user signs into the system. According to Expert 12, \"There must be several layers of security, such as having a fingerprint or face ID; it is feasible to send the OTP, but it will not be like the patient's fingerprint or face... It is required because it may be possible to steal the patient's device and try to log in and get the code\". Privacy is also critical, and this requirement is achieved by applying access control through Hyperledger Fabric. * Interoperability  
In healthcare, interoperability generally focuses on data sharing among business organizations [66]. Patient-driven interoperability occurs when a patient's data are made available via specific standards [67]. With this approach, the patients approve the exchange of health data with trusted institutions as supervisors. Thus, the data formats should comply with consistent standards [67; 68; 69; 70]. According to Experts 2 and 3, there must be a unification of medical data standards for all healthcare centers. Each healthcare center follows a different school in terms of reading and classifying the data. In addition, nonunified medical data standards lead to the low interoperability of medical information systems among healthcare providers [2]. * User friendliness and efficiency  
The system should allow users to complete their tasks efficiently, and it should have a user-friendly graphical interface [71]. Therefore, a user-friendly interface will enhance the usage of the system so that patients can make reservations and physicians can perform their work easily [71]. As Expert 6 illustrates, \"The system should be easy to use. Now I waste some time due to the difficulty of navigating between pages; automatic saving and filling fields are essential\". Expert 2 says, \"It should be efficient and fast. I mean, when data are retrieved, there should not be a hiccup\". Table 2 illustrate summery of PHR requirements.