## 3 Related Work  
### Access Control and Data Ownership  
Electronic health records (EHRs) and PHRs allow physicians and healthcare providers to access and review their patients' health histories electronically. Various studies have been pursued to allow patients to control, own, and share their data. [PERSON] et al. [24] proposed a system with two models based on a private Ethereum network to allow patients to own their data. First, there is a linkage model on the healthcare center's side that links EHRs to the blockchain to create a touchpoint for patient visits. Second, there is the request model, where patients provide permission for a clinic's physician and then add them to the authorized list. A patient also has the option to reveal what information the physician can view and can choose the data they wish to reveal. However, the system has scalability constraints. [PERSON] et al. [25] developed a system to manage patient data from reports or IoT devices; the solution is based on Hyperledger Fabric and Composer. The solution focuses on collecting data from IoT devices to monitor a patient's vital signs, allowing the physician make the right decision at the right time. The patient has complete control of their EHR, and the physician must request permission to view it. Similarly, [PERSON] et al. [26] proposed a blockchain-based personal health information management system that allows users to have complete control over their data and the sharing of their data from their medical IoT devices. The system focuses on an adapter component that collects data from the backend of a wearable health device and sends it to the blockchain for storage rather than a provider's cloud storage. Another work, by [PERSON] et al. [27], proposed a high-level architectural solution for collecting and sharing health data while assuring immutability and data privacy. Following GDPR compliance, each patient has the right to be forgotten in terms of their data. Another solution for cross-institution and medical data sharing with highly secure data sharing was proposed by [PERSON] et al. [28]. The system is built on the Ethereum framework and has two sorts of access based on incentives to allow patients to benefit from sharing their data. Non-incentive access is normal access provided to a physician, who can then view a patient's record. The incentive model is for researchers or marketing companies using these data for non-medical purposes. [PERSON] et al. [29] designed architecture for EHRs to ensure secure and private communication across various stakeholders utilizing Hyperledger Fabric. The proposed solution gives a patient access control over their record. The solution provides a general overview of how patients will manage their reports and how blockchain will be utilized. However, a deeper look is needed to address the real requirements for stakeholders and what kind of permissions and restrictions they must have. Another work, by [PERSON] et al. [30], designed and implemented scenarios based on a Hyperledger Fabric consortium after determining the general requirements for EHRs. The authors present experiments and illustrate how the system complies with the GDPR, achievingsecurity, privacy, and confidentiality by storing all data on-chain and providing access control. Considering the user's perspective, [PERSON] et al. [11] developed three principles that should be considered when developing solution-based PHRs. First, the data structure should be unified in order to be easily integrated into the existing ecosystem. Second, the implementation should have a safe, reliable, and traceable infrastructure to prevent unauthorized access; finally, it should have an easy-to-use access control mechanism. The authors continued their work by developing an operational prototype based on a private blockchain and a Hyperledger Fabric framework. The authors recommended considering these principles in future works and utilizing consortium blockchain and stakeholder engagement. Other studies engaged stakeholders to understand their needs.