# Overview of Blockchain Oracle Research
## 4 Results
### Publications by Outlets and Publishers  
As Figure 4 shows, the majority of papers published in this field are journals (73) and conference papers (60). However, a small portion consists of book sections (20) and preprints (9). These data contrast previous blockchain technology reviews, showing that the number of conference contributions is four times more than that of journal publications [2; 16].  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Country** & **OT** & **OA** & **Total** \\ \hline China & 10 & \(13\) & 23 \\ Italy & 7 & 11 & 18 \\ USA & 11 & 4 & 15 \\ Canada & 7 & 8 & 15 \\ Germany & 7 & 7 & 14 \\ UAE & 1 & 12 & 13 \\ Australia & 7 & 2 & 9 \\ France & 2 & 3 & 5 \\ Austria & 4 & 0 & 4 \\ India & 2 & 1 & 3 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Distribution among the ten most productive countries.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Continent** & **OT** & **OA** & **Total** \\ \hline Europe & 31 & 36 & 67 \\ Asia & 18 & 35 & 53 \\ America & 18 & 12 & 30 \\ Oceania & 8 & 2 & 10 \\ Africa & 0 & 2 & 2 \\ \hline \hline \end{tabular} \(\mathrm{OT}=\) oracle theory; OA = oracle applied.  
\end{table}
Table 5: Distribution by continent.  
This finding supports the idea that there seems to be no dedicated conference venue on blockchain oracles. Table 6 and Figure 5 show the distribution of papers by journal and publisher, respectively. We observed that the majority of papers (61) are published in IEEE outlets and venues, whereas 25, 15, and 13 papers are published in Springer, Elsevier, and MDPI, respectively. However, if we consider only journal publications, the weight of the contributions would slightly change, given that 43 IEEE documents were conference papers, and of 25 Springer entries, 20 were book sections.  
Then, excluding non-journal publications, we would have IEEE with 18 publications, followed by Elsevier with 15, MDPI with 13, and Springer with 5. This information is incredibly insightful when considering Table 7, which shows that only four journals published more than two papers on the subject. Conference venues and book sections, except for two venues, contributed no more than one document.  
\begin{table}
\begin{tabular}{c c c} \hline \hline  & **Journal/Venue Name** & **Publisher** & **Contributions** \\ \hline \multirow{4}{*}{Journal} & _IEEE Access_ & IEEE & 8 \\ \cline{2-3}  & _Future Generation Computer Systems_ & Elsevier & 8 \\ \cline{2-3}  & _Applied Sciences_ & MDPI & 3 \\ \cline{2-3}  & _IEEE Internet of Things Journal_ & IEEE & 3 \\ \hline \multirow{4}{*}{Conference} & 2019 IEEE International Conference on Blockchain & \multirow{4}{*}{\begin{tabular}{c} IEEE \\ 2021 IEEE Information Theory Workshop (ITW) \\ \end{tabular} } & \multirow{4}{*}{\begin{tabular}{c} IEEE \\ 2021 IEEE Information Theory Workshop (ITW) \\ \end{tabular} } \\ \cline{2-3}  & \
\begin{tabular}{c} Business Process Management: Blockchain and \\ Robotic Process Automation Forum \\ \end{tabular} & Springer International & 5 \\ \cline{2-3}  &
\begin{tabular}{c} Financial Cryptography and Data Security. FC \\ 2021 International Workshops \\ \end{tabular} & Springer Berlin Heidelberg & 2 \\ \hline \end{tabular}
\end{table}
Table 6: Documents by Journal/Venue.  
Figure 4: Publications per type.  
As shown in Table 6, the journals that published more contributions are _IEEE Access_ and _Future Generation Computer Systems_, both with eight contributions. Among the other venues, the only notable is _Business Process Management: Blockchain and Robotic Process Automation Forum_, which contributed five book chapters.