## 3 Related Work
### Access Control and Data Ownership
[PERSON] et al. [31] developed an EHR data-sharing framework based on Hyperledger Fabric, where cancer patients can share their data and give access to physicians, who are constrained by time. The storage of large amounts of data is off-chain to avoid scalability issues. However, the study does not cover emergency access. Moreover, only one orderer was applied, and this was considered a single point of failure. Another solution integrates cloud computing within the blockchain. For instance, [PERSON] et al. [32] proposed a generic EHR model by mixing private and public blockchains so that patients can share their data. However, scenarios or prototypes based on real frameworks should be addressed to support such claims. Another work, by [PERSON] et al. [33], presented a high-level architecture for sharing data among healthcare stakeholders after patient permission is provided. The authors illustrated a proof of concept based on a private Ethereum blockchain. Another work, by [PERSON] et al. [34], presented a general reference architecture for PHRs. According to the authors, the architecture was designed after analyzing the current application of health records, and they illustrated how patients can have access control by adopting blockchain technology. However, the requirements were not illustrated for either the stakeholders or the patients, and the type of framework that should be utilized was not given. From another angle, in the traditional emergency system, patients cannot provide access permission to emergency personnel to access their PHR. In some cases, a patient may transfer their record from healthcare centers where no medical record belongs. Few studies have been conducted to overcome this issue. [PERSON] et al. [35] proposed a simple framework for a patient emergency access control system that defines permission access rules through Hyperledger Fabric. Patients can determine access to their data in emergency conditions by setting an authorization access control policy for their data through a developed smart contract. Thus, in an emergency, the medical staff does not need to contact a patient's relatives or wait for a third party to approve access to their data. In contrast, the patient determines and defines an access control policy for their data by enabling an emergency physician to access their data for a limited time to ensure patient privacy. Based on the storage of off-chain data in a decentralized file system, in [36] a healthcare data sharing system was proposed to overcome the performance and scalability issues of centralized databases. The study mainly focused on the performance analysis of a network considered for an emergency case of a patient, since traditional and off-chain-based cloud databases need to be much faster and scalable. The authors proposed a blockchain-based architecture containing three types of smart contracts: registry contracts for system protection from malicious users, data contracts for records storage, and permission contracts for access permission. The experiment showed better results compared to a traditional approach. However, the mechanism for how emergency conditions will be performed was not clarified in the architecture or even described.