# Centralized vs. Decentralized: Performance Comparison between BigchainDB and Amazon QLDB
## 2 Literature Review  
In order to provide a more comprehensive understanding of this research topic, we have reviewed the scientific literature based on the Web of Science, IEEE Explore, Scopus, ScienceDirect, Wiley, and Google Scholar scientific database. We have used search keywords, such as \"centralized ledger\" or \"centralised ledger\" and \"decentralized ledger\" or \"decentralised ledger\", in order to identify the relevant research articles, studies and chapters. Table 1 presents the search queries in the explored databases that are limited to the title, abstract and keyword fields of scientific publications. There were no restrictions in terms of the publication dates. The query results from each of the selected scientific databases are listed in Table 2 and have been graphically illustrated in Figure 1.  
In order to search for grey literature (scientific literature that is produced outside of traditional publishing, distribution and indexing venues), we have used the Google Scholar database due to its broader coverage of articles and publications, including academic articles, theses/dissertations, conference proceedings, books or book chapters, unpublished materials (such as preprints), and other types of documents (i.e., non-academic articles) [5; 6]. The number of publications indexed in the Google Scholar database referencing the term _centralized/centralised ledger_ is 1260, while for _decentralized/decentralised ledger_, the number of scientific publications is 6540. Consequently, this fact proves an increased interest in these topics. However, given the fact that there are large differences in terms of the number of publications indexed in Google Scholar versus the number of scientific publications indexed in other databases, this database has not been given any consideration in this analysis. The annual evolution of the number of scientific papers indexed in each of the selected databases referencing the above-mentioned keywords is shown in Tables 3 and 4, as well as in Figure 2a,b. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Database** & **Centralized Ledger** & **Decentralized Ledger** \\ \hline Web of Science & (TS = (“centralized ledger”) OR TS = (“centralised ledger”)) & (TS = (“decentralized ledger”) OR TS = (“decentralised ledger”)) \\ \hline IEEE Xplore & (“All Metadata”:“centralized ledger”) OR (“All Metadata”:“decentralized ledger”) OR (“All Metadata”:“centralised ledger”) & Metadata”:“decentralised ledger”) \\ \hline Scopus & (TITLE-ABS-KEY (“centralized ledger”) OR & (TITLE-ABS-KEY (“decentralized ledger” OR \\ TITLE-ABS-KEY (“centralised ledger”)) & TITLE-ABS-KEY (“decentralised ledger”)) \\ \hline Science Direct & “centralized ledger” OR “centralised ledger” & “decentralized ledger” OR “decentralised ledger” \\ \hline Wiley & “centralized ledger” OR “centralised ledger” & “decentralized ledger” OR “decentralised ledger” \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Search queries in scientific databases. Figure 1: Number of articles found in each of the selected scientific databases. Although academic literature investigating the industrial applications of centralized and decentralized ledgers has recently grown in volume ([7,8]), the findings have shown that the number of publications aimed at a better understanding of the use of these ledgers and their applications is still insignificant. The analysis of the above results indicates that, with the exception of the current year of 2022, there has been an increasing trend in the number of academic publications from ScienceDirect that reference the centralized and decentralized ledger. This trend reflects the scientific community's growing interest and satisfies the industry's needs. However, the traditional approach of using databases is still an important component of today's technological landscape. Moreover, there is competition between the LT-based technologies themselves, with both centralized and decentralized being used in the products that are based on the LT technology.