# Overview of Blockchain Oracle Research
## 4 Results
### Article Type, Fields, and Keywords  
Table 7 provides an overview of the paper types determined by fields based on the main categories and sub-categories indicated in Section 3.1. It emerges as more than half (103); precisely, 63% are empirical papers, 23% are theoretical papers, and 14% reviews. At \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Field** & \multicolumn{3}{c}{**Article Type**} & **Total** \\ \hline \multirow{2}{*}{**Main Categories**} & **Subcategories** & **Empirical** & **Theoretical** & **Review** \\ \hline \multirow{3}{*}{Oracle Theory} & Oracle Problem & 6 & 6 & 18 \\ \cline{2-5}  & Proposal & 19 & 3 & 0 & 22 \\ \cline{2-5}  & Architecture & 18 & 8 & 9 & 35 \\ \hline \multirow{3}{*}{Oracle Applied} & Finance & 16 & 2 & 4 & 22 \\ \cline{2-5}  & Data Management & 9 & 5 & 0 & 14 \\ \cline{2-5}  & IoT * & 9 & 2 & 1 & 12 \\ \cline{2-5}  & BPM * & 4 & 3 & 1 & 8 \\ \cline{2-5}  & Supply Chain and & & & & \\ \cline{2-5}  & Traceability & 6 & 1 & 1 & 8 \\ \cline{2-5}  & AI * & 4 & 3 & 0 & 7 \\ \cline{2-5}  & Cloud Computing & 4 & 1 & 0 & 5 \\ \cline{2-5}  & Healthcare & 4 & 0 & 0 & 4 \\ \cline{2-5}  & Transport & 2 & 2 & 0 & 4 \\ \cline{2-5}  & Energy & 2 & 1 & 0 & 3 \\ \hline \hline \end{tabular}  
* IoT = Internet of things; BPM = business process management; AI = artificial intelligence.  
\end{table} 
Table 7: Distribution by category and article type. Figure 5: Documents by publisher. the general level, the majority of academic research over oracles is of an empirical nature. Nevertheless, these data still need to be distinguished by field of research. Concerning division by category, despite the higher number of sub-categories, the total number of papers belonging to OT (75) is slightly below those on OA (87). This is understandable, considering that oracles are still in their early-stage development, and a heterogeneity of views on how they should function and operate still exists. Although the majority of articles are still empirical, they are well balanced with theoretical and review types for the \"architecture\" and \"oracle problem\" sub-categories. The second thing that emerges is that proposals are mainly of empirical/experimental nature, which bodes well for the birth of oracle frameworks in cooperation among or fully developed by academic institutions. Regarding \"oracle applied (OA)\" papers being ideally a more practical area compared to OT, why an imbalance (except for BPM, AI, and transport) exists between empirical and theoretical papers is understandable. Furthermore, the smaller category size explains why only seven review papers were retrieved. By analyzing sub-categories, we can observe that some areas have fewer contributions than others. The finance sector leads with contributions, with 22 contributions, followed by data management (14) and IoT (12). Given the higher advancement level of blockchain applications in these sectors and the empirical nature of academic contributions, why other sectors, such as healthcare, transport, and energy, have less than five contributions is also understandable. Keywords are also an important parameter to consider when evaluating a sample. A total of 650 keywords were extracted from the sample, which means a media of 3.9 per article. While some articles had six or more keywords, others (mainly preprints) had none. After duplicates and plurals were removed, 307 unique keywords were found. To avoid biases with the research strings used, however, we excluded keywords such as \"blockchain\" and \"oracle(s)\" from the analysis. Keywords composed of multiple words (e.g., Smart Contract) were considered unique, and those composed of banned keywords, such as \"price-oracles\", were not excluded. The choice to leave keywords composed of the two banned words lies in the idea that, while those keywords alone are common for all papers, composed keywords, such as centralized oracle or blockchain interoperability, are proper in specific sectors, which will benefit from homogeneous keyword usage.