# Structuring Reference Architectures for the Industrial Internet of Things
## 4 Selecting the Reference Architectures  
The selection of noteworthy reference frameworks needs to be based on the interest of the target groups from the industry and research. One way to quantify this interest is based on the number of searches done via internet search engines, mainly Google. The following assumptions underlies the process of determining this interest: (a) Only broadly known reference frameworks are able to create the necessary impact and (b) the interest in the respective framework is more accurately indicated by the name of the publishing organization (for instance 'Industrial Internet Consortium') rather than the name of the reference architecture ('Industrial Internet Reference Architecture'). In particular the second assumption is based on a previously conducted literature search and results in a higher precision. 'Plattform Industrie 4.0', 'Industrial Internet Consortium', 'Industrial Data Space' and 'Industrial Value Chain Initiative' were the seed searches. The other approaches were iteratively added during the literature research and as returned by the named search engines. Table 1 gives an estimation of the impact on the research community and the overall interest. Google Scholar statistics give a rough impression of the influence based on mentions in research publications. The collected dimensions are reflecting the mentioning of the respective terms in the whole indexed literature and in the papers published from April 2018. In addition, the total amount of citations of the main reference architecture publication have been counted wherever possible. The aggregated rank (Table 1) equally reflects the academic relevance through references and citations, on the one hand and the popularity in the Google Trends list on the other. One can easily recognize that the more industry-driven architectures have significantly less citations but tend to be more popular in terms of web searches. \begin{table}
\begin{tabular}{l c c c c c c c c c} \hline \hline
**Framework** & **Description** & **Description** & **Description** & **Description** & **Description** & **Description** & **Description** & **Description** & **Description** \\ \hline OpenFog & 558,000 & (5) & 17,600 & (5) & [23] & 23 & (6) & 3 & 2 & 1 \\ \hline IIC & 181,000 & (7) & 12,300 & (7) & [3] & 74 & (2) & 1 & 7 & 2 \\ \hline Platform Industrie 4.0 & 17,000 & (10) & 4340 & (9) & [24] & 57 & (3) & 5 & 6 & 3 \\ \hline IDS & 4,480,000 & (2) & 101,000 & (1) & [25] & 14 & (8) & 2 & 10 & 4 \\ \hline x-Road & 3340 & (14) & 288 & (15) & [26] & 46 & (4) & 10 & 3 & 5 \\ \hline FIWARE & 2740 & (15) & 566 & (13) & [27] & 18 & (7) & 12 & 1 & 5 \\ \hline Industrial Value Chain & 4,590,000 & (1) & 22,100 & (3) & [28] & 3 & (12) & 8 & 8 & 7 \\ \hline Industrie du Futur & 125,000 & (8) & 5130 & (8) & [29] & 0 & (13) & 13 & 4 & 8 \\ \hline IoT-Architecture & 6680 & (11) & 2540 & (11) & [30] & 239 & (1) & 4 & 13 & 8 \\ \hline Open Connectivity Foundation & 1,330,000 & (4) & 19,200 & (4) & [31] & 9 & (9) & 6 & 11 & 8 \\ \hline BDVA & 4,150,000 & (3) & 32,300 & (2) & [32] & 4 & (11) & 7 & 12 & 11 \\ \hline Edgecross & 5950 & (12) & 330 & (14) & [33] & 0 & (13) & 15 & 5 & 12 \\ \hline Arrowhead Framework & 37,900 & (9) & 3490 & (10) & [34] & 36 & (5) & 9 & 13 & 13 \\ \hline Piano Industria 4.0 & 5570 & (13) & 691 & (12) & [35] & 7 & (10) & 14 & 9 & 14 \\ \hline Alliance of Industrial Internet & 291,000 & (6) & 16,500 & (6) & [36] & 0 & (13) & 11 & 13 & 15 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Ranking of selected IIoT reference frameworks ranked by Google Scholar (research relevance) and Google Trends (public interest) appearance. The combination of the outlined measures indicates the impact and importance of the respective frameworks. The noted overall rank, therefore, supplies a rough impression of the significance of a framework in relation to the other frameworks. The interested user can better estimate the value of the provided specifications in terms of its innovative potential but also the possible community impact.