# Blockchain Application in Internet of Vehicles: Challenges, Contributions and Current Limitations
## 3 Review Method
### Reporting the Review
Other application areas made up around 22% of the total, as presented in Figure 7.  
From the abovementioned facts, it is obvious that the impact of blockchain in smart grids and especially in the car industry has been widely assessed. Blockchain is now receiving more attention in the IoV sector, where its transformative potential also appears impressive, as will be presented in Section 4. This led the authors to further investigate the blockchain adoption in each one of the identified IoV application areas. The authors gathered this kind of information following an algorithmic approach, leveraging an algorithmic model, based on web-harvested information for assessing the blockchain's correlation with different applications (e.g., charging management, pricing schemes, etc. ), as initially described in [35]. In this model, the basic idea is to apply web mining techniques to estimate the strength of association between two words/terms. This approach has been widely used in areas such as information retrieval and natural language processing, which deal with (mostly) textual data, while the world wide web (www) is regarded as the largest possible source of data. Based on the latter hypothesis (i.e., www as the largest source), the use of appropriate tools, both for indexing and querying, is needed. For this purpose, the employment of standard search engines--through their respective APIs--constitutes a common practice. Motivated by the above considerations, we used the Google web search engine. For every application (Table 3), an association score was computed between this application and the term \"internet of vehicles\". For example, for the \"pricing scheme\" application, the association score was computed by calculating the Pointwise Mutual Information (PMI) between \"pricing scheme\" and \"internet of vehicles\", taking into account the number of hits (i.e., the number of search results) as returned by the used web search engine. More details about PMI can be found in the indicative works of [36; 37], where in the latter, PMI is applied over www data. The results are shown in Table 3. It appears that higher positive scores indicate a stronger association, while scores that lie closer to 0, as well as negative scores, suggest weaker associations. Figure 5: Distribution of studies from 2017 to 2021. In terms of the results, as also depicted in Figure 7, blockchain technology is currently widely adopted in the areas of ride sharing, studies on energy consumption and pricing schemes that are related with different IoV participants. It is also observed that there is a significant correlation of blockchain in the areas of charging management, V2X communications, traffic control and data protection. The correctness of the aforementioned scores and observations is also justified by the literature, considering that they are included in the top \begin{table}
\begin{tabular}{c c} \hline \hline
**Application Area** & **Correlation Result** \\ \hline Ridge sharing & 1.499 \\ Energy consumption & 1.121 \\ Pricing schemes & 1.049 \\ Data protection & 0.491 \\ Charging management & 0.468 \\ Traffic control & 0.415 \\ V2X communication & 0.300 \\ Demand response & 0.095 \\ Machine learning & 0.047 \\ Incentive mechanisms & \(-\)0.032 \\ Identity management & \(-\)0.157 \\ Network performance & \(-\)0.369 \\ Regulation & \(-\)0.398 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Association of blockchain in different IoV application areas: results. Figure 6: Blockchain application areas in the IoV. Figure 7: Blockchain applications in the IoV—classification according to their application areas. three categories, as depicted in Figure 7. On the other hand, for the areas that had a negative score or a score close to zero (e.g., demand response, incentive mechanisms, network performance, etc. ), it is believed and justified--both from the web mining process and from the literature--that they do not have a high blockchain adoption rate yet. This is justified by their weak association rate with blockchain.