# Overview of Blockchain Oracle Research
## 5 Converging Studies, Research Themes, and Research Directions
### Oracle Theory  
Subjects pertaining to the OT and the oracle architecture comprise many different studies. Given that oracles are a niche area of investigation, they are not officially classified by type, and their characteristics have yet to be defined. A group of studies has been dedicated to investigating common patterns that emerge from oracle architectures, with the aim of classification and improvement [67; 68; 69; 70; 71]. [PERSON] et al. [67] differentiated reputation-based and voting-based oracles, explaining how each design provides the answer to the smart contract. [PERSON] et al. [68] instead distinguished oracles between inbound and outbound, depending on the direction of the data flow (push and pull). Inbound oracles provide data to the blockchain, whereas outbound ones transfer data from the blockchain to the real world. Specific examples are also made of blockchain applications, where data are pushed or pulled into the smart contract. [PERSON] et al. and [PERSON] et al. built a framework to select the most appropriate oracle design (in terms of security and data management) according to different blockchain applications [32; 69; 71]. Other works from the University of Colorado [72], Jiamusi University [73], and Hong Kong University [74] focused on the security and privacy challenges of Oracle-based smart contracts. Their research study mainly examined how to identify and prevent oracle malfunction (integrity), guarantee that data collected is exploited solely by the smart contract (confidentiality), and prevent downtime or censorship attempts (availability). A group of works from Montana State University [75], University of Sfax [76], and the University of Cagliari [77] focused instead on oracle fees and gas-price oracle malfunctions. The work of Montana State University investigated the reasons that led to gas price oracle failures, and the study from the University of Cagliari outlined the failure rate of gas price oracles with an empirical approach. The paper from the University of Sfax compared different gas-pricing techniques with the aim of improving oracle reliability. Another central subject in OT is the oracle problem issue, for which many contributions were retrieved. A group of papers focused on explaining the oracle problem, whereas others focused more on empirically investigating the subject to overcome the issue. Two papers from the University of Ljubljana and Max-Planck Institute introduced the oracle problem from a legal point of view [29; 30]. In this paper, the oracle's role as legal actors and their responsibility as a trusted entity were investigated. A similar discussion can also be retrieved in [PERSON] et al. [78], which, however, focused on the legal audit of smart contracts. A thorough discussion of the audit of the smart contract in light of the oracle problem could instead be found in two works by [PERSON]. [13; 79], which first introduced the problem of auditing contracts and then offered insights for future auditors to perform the task better. Other papers from the University of Verona and Khalifa University focused on investigating trust models and the consequences of having untrusted oracles in various sectors, such as Intellectual Property Rights (IPRs), DeFi, and supply chain [6; 9]. Considering the amount of money managed by DeFi platforms, the financial implications are alarming [14; 46]. Singapore University has also confirmed this result with research focused on investigating the reliability of oracles in DeFi applications [1]. Finally, studies from the Chiba University of Technology and the University of Dallas explored, with empirical data, the incentives of oracles to cheat or fail to transmit information [80; 81]. The focus of these studies has mainly concerned the issue of how trust can be built or undermined in digital economies and how collective intelligence helps prevent selfish individuals from performing disruptive actions in the community. The last subject of OT pertains to oracle proposals.