# Overview of Blockchain Oracle Research
## 5 Converging Studies, Research Themes, and Research Directions
### Oracle Applied
[115] proposed an ad hoc blockchain architecture based on sharding and a peer-to-peer oracle network in order to manage IoT devices. Although at an early stage, the prototype already shows some experimental results. As for cloud computing, only five studies were retrieved. Two were published at the University of Ljubljana and focused on how oracles can enhance trust and efficiency in a cloud computing platform. Defining the drivers of trust, a trust management scheme is proposed to show how a trusted data flow can be achieved between application components (e.g., camera, fog node, and cloud storage) [66]. In subsequent work, the research is extended, showing how oracles can increase scalability and cost-efficiency in federated edge-to-cloud computing environments by allowing transactions to be executed off-chain [116]. [PERSON] and [PERSON] [117] also proposed introducing a computing oracle to reduce on-chain network usage. In line with these studies, [PERSON] et al. [118] proposed oracles as a monitoring service for service-level-agreement violations in cloud environments. Utilizing a Stackelberg differential game, they also investigated the perfect balance between quality verification requests and monitoring prices. A consistent group of papers applied oracles for data management. [PERSON] et al. [119] investigated how oracles impact data quality in terms of the timeliness, costs, and availability of data. They showed that availability increases by querying an external oracle service, but so do also costs. [PERSON] et al. [120] proposed a reputation system to reward better-performing oracles to improve accessibility and costs, eventually increasing data quality. In a subsequent study, the authors better specified the drivers to discover trusted and better-performing oracles, also showing simulation results [121]. Other authors have focused on data communication between blockchains. [PERSON] et al. [122] proposed DE-PEG, a modification of the PEG algorithm said to reduce the cost of data availability oracles and thought to also prevent stalling attacks. [PERSON] et al. [123] explored active communication between blockchains through oracles, specifying which type of data should be transmitted. However, in their research, they assumed that the oracle is always trusted, so they also did not provide a scheme to prevent oracle data manipulation. Finally, [PERSON] [124] proposed HBRO, an oracle system that enables communication between permissioned and permissionless blockchains concerning digital rights management (DRM). Once DRMs are elaborated on the permissioned chain, they are securely transmitted through the data oracle to a permissionless blockchain with a notary mechanism. Works in the transport sector have focused on the security, privacy [125; 126], and efficient identification of vehicles [127], as well as data processing for intensive transport environments, such as commercial waterways [128]. Whereas the works from Khalifa University and Guangxi University discussed the implementation of Chainlink for autonomous vehicle test-case repositories and identification, the works from other universities proposed their own oracle design for efficient data transmission in the transport industry. Finally, three entries were retrieved for the energy sector. All three were published between late 2021 and early 2022. The shared vision aims at decentralizing the energy market, but with a different focus. [PERSON] et al. [129] proposed an energy flexibility token to incentivize renewable energy production at the local level. [PERSON] et al. [130] implemented a decentralized oracle system and zkSNARKs to improve renewable energy certificate allocation. Lastly, [PERSON] et al. [131] investigated efficient oracle designs to guarantee secure and unforgeable data transmission between actors involved in the energy market. An overview of the above-mentioned results can be found in Table 13.