# Overview of Blockchain Oracle Research
## 6 Discussion  
The literature review showed some interesting insights about themes covered by the existing studies and areas that require more attention. Although a group of studies have tried to classify oracles, the very concept of oracle is still not clearly defined. Oracles are generally identified as data-feeding ecosystems, which can come in various forms or structures, but if this is the purpose of oracles, then anything that provides data for a blockchain is an oracle. Therefore, rollups or bridges should also be considered oracles. We could argue, for example, that the lighting network is an oracle for the bitcoin network, but then we may also have oracles on the lighting network. Therefore, the boundaries of what can be defined as an oracle should be clearly settled. The classification of oracles is also quite heterogeneous, and it often reduces the clarity of the presented research. In addition to software and hardware, we also have reverse, centralized, decentralized, computation, consensus, and voting-based oracles. Often, they refer to the same type with different names or to different types with the same name (e.g., decentralized and consensus-based oracles). Similarly, the issue of having trusted entities in trustless environments, often referred to as the \"oracle problem\", has also been labeled in some research as the \"oracle paradox\". Likewise, the coexistence of inbound and outbound oracles is referred to equally as the \"dual-oracle problem\" or \"dual simplex communication\". Therefore, efforts should be made in this regard so that research can build on a common oracle taxonomy. Concerning the investigation of oracle trust models, this seems to still be a niche field, and despite the few contributions, the very concept of trust lacks a broader discussion and clarification. Indecisiveness on whether an oracle should be trustless or \"provably honest\" is apparent, which is, in theory, not really the same concept. With regard to oracle proposals, they are heterogeneous, but almost all focus on decentralized or consensus-based oracle systems. Centralized oracles, such as the ones proposed in [124; 132; 133], should also be worthy of investigation. For certain data types that are not in the public domain and where data sources are limited, a centralized and secure data channel would be more appropriate than a slow, expensive, and probably less secure decentralized oracle type. A trusted oracle is indeed a single point of failure, but it is undoubtedly more efficient as long as it resists attacks and behaves honestly. Therefore, more research is expected and needed in that direction. Furthermore, despite the plethora of emerging oracle solutions on the market, on the academic side, the trend is to propose a new oracle solution or utilize only the most known or advertised ones (e.g., Chainlink or Provable). Therefore, an exploration of emerging oracle solutions by academic researchers is expected and required. Another issue that emerged in this study is that studies concerning oracle solutions for DRM, such as the one by [PERSON] [124], are limited. As the original idea of blockchain proposed by [PERSON] and [PERSON] [55] was to authenticate digital documents, more attention to this sector was also expected in blockchain oracle research. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Research Themes** & & **Research Directions** & **Converging Studies** \\ \hline  & & **Finance** & \\ \hline  & & **Transport** & \\ \hline \multirow{3}{*}{Vehicle management} & - & Guarantee privacy in the vehicle & Khalifa University [125] \\  & - & identification & Guangxi University [127] \\  & - & Process autonomous vehicle data & \\ \hline \multicolumn{3}{c}{**Energy**} \\ \hline \multirow{2}{*}{Energy market management} & - & Incentivize renewable energy production & Technical University of Cluj-Napoca [129] \\  & - & Improve privacy in the energy market & Technical University of Munich [130] \\ \hline \hline \end{tabular}
\end{table}