# Overview of Blockchain Oracle Research
## 3 Methodology
### Data Extraction  
Appropriate extraction variables (displayed in Table 3) were identified to extract as much information as possible from the selected sample. As this is probably the first bibliometric analysis on blockchain oracles, building upon existing or prior research was impossible. However, given that the aim of bibliometric analyses is relatively homogeneous, extraction variables could be taken from similar papers investigating other literature domains [24; 56; 59]. First, the \"year of publication\" was considered to place the literature within a specific timeframe, whereas the \"element type\" shows the most usual outlet for retrieved publications. \"Authors\", \"institutions\", and \"countries\" of provenance geographically contextualize the paper sample, highlighting the contributors to the academic advancements in the sector. Citations and keywords were used to analyze metrics. Finally, as in [PERSON] and [PERSON] [24], articles were further divided based on their specific fields of analysis. This categorization of papers serves to investigate whether streams of literature exist where researchers are more contributing and others that require more attention. Although it may constitute a bias, in line with prior research, articles were associated with only one field category to avoid double entries [24]. First, two main categories were identified, \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Steps** & \multicolumn{3}{c}{**Databases**} & **Total** \\ \hline  & **Scopus** & **Web of Science** & **Google Scholar** & \\ \hline Papers are retrieved using & & & & \\ research strings & & & & \\ \hline Off-topic papers are & & & & \\ removed & & & & \\ \hline Duplicates are removed & & & & \\ \hline Unrelated papers are & & & & \\ removed & & & & \\ \hline Final sample & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Research Steps. \begin{table}
\begin{tabular}{c c} \hline \hline
**Variable** & **Description** \\ \hline Category & The research field of analysis \\ Item Type & Journal, conference, book chapter, or preprint \\ Year & Year of publication \\ First Author & Name of the first author \\ Authors & Full author list \\ Title & Title of the paper \\ Citations & Google Scholar citations \\ Outlet & Name of the journal/conference/book \\ Publisher & Name of the publisher \\ Keywords & Indexing keywords \\ Country & Country of the first author \\ Continent & The continent of the first author \\ Institution & Institution of the first author \\ Study type & Theoretical, empirical, or review \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Extraction variables. mainly to distinguish between studies concerning oracles themselves and oracles applied to other sectors. Second, the papers were divided to further differentiate them based on their specific fields of analysis. Although inspired by related research, category selection embodies a certain degree of subjectivity. Therefore, a description of these categories, starting with the main ones, is provided hereafter. Oracle Theory (OT): Under this category, papers specifically focused on blockchain oracles, either from a theoretical or a practical point of view, were included. Oracle Applied (OA): This category included papers that focused on real-world applications, such as healthcare, finance, and business process management, and also provided a detailed analysis of the role of oracles in these fields with theoretical or experimental approaches. The main categories were further divided into sub-categories. Hereafter, those that belong to OT are listed as follows. Architecture: With an empirical or theoretical approach, papers in this category performed analyses on the oracle framework to improve technical aspects, highlight current challenges, and identify new avenues for research. Unlike proposals or OA papers, this group includes works that have investigated existing oracle schemes that are not directly applied to a specific sector.