## 3 Publication Structure Analysis
### Web of Science Categories and Indexed Publications  
Figure 9 shows the number of OT security papers categorized by WoS and their respective totals. The category with the most publications, reaching a total of 458, is 'Computer Science Information Systems', followed by 'Engineering Electrical Electronic' with 427 papers. A notable focus on OT security within computer science domains is evident, as six of the top ten WoS categories are associated with computer science. The categories, specifically 'Computer Science Theory Methods', 'Computer Science Hardware Architecture', 'Computer Science Artificial Intelligence', 'Computer Science Interdisciplinary Applications', and 'Computer Science Software Engineering', were ranked third (355 publications), fifth (141 publications), sixth (125 publications), seventh (123 publications), and eighth (109 publications), respectively. 'Telecommunication', with 221 articles, occupies the fourth position. In the top ten categories, the bottom two spots are held by 'Automation Control Systems' and 'Engineering Multidisciplinary', with 93 and 55 published papers, respectively. The distribution of publications across several categories in Computer Science, excluding the highly rated 'Computer Science Information Systems' and 'Computer Science Theory Methods', is relatively equal. \begin{table}
\begin{tabular}{c c c c} \hline
**Research Area** & **Proceeding Paper** & **Article** & **Review Article** \\ \hline Computer Science & 461 & 367 & 16 \\ Engineering & 239 & 282 & 17 \\ Telecommunications & 104 & 111 & 6 \\ Automation Control Systems & 65 & 27 & 1 \\ Physics & 2 & 41 & 1 \\ Chemistry & & 33 & 3 \\ Instruments Instrumentation & 8 & 24 & 3 \\ Science Technology Other Topics & 12 & 19 & 2 \\ Energy Fuels & 19 & 9 & 2 \\ Materials Science & 1 & 25 & \\ \hline \end{tabular}
\end{table} 
Table 2: Distribution of publications by research area and paper category. Figure 9: Web of Science categories from 1124 OT publications from the Web of Science database. Figure 10 illustrates the publication trends in various WoS categories from 2014 to 2024. In 2021, Computer Science Information Systems saw the largest volume of published documents. It remained a dominant category in 2019, 2020, 2022, 2023, and 2024, although absolute numbers are lower. 'Engineering Electrical Electronics' and 'Computer Science Theory Methods' kept the second and third places in recent years since 2019, except in 2024, when 'Telecommunications' took the third place, pushing out 'Computer Science Theory Methods'. This shows the growing importance of this area while Computer Science categories start decreasing. Figure 11 provides a comprehensive examination of the different document types produced in OT security within certain WoS categories. A steady increase in the number of publications can be observed in research articles and conference proceedings, while the number of review articles remains vanishingly small except 'Engineering Electrical Electronics' and 'Computer Science Information Systems' categories, with 12 and 10 articles, respectively. Figure 12 illustrates the number of OT security publications within the WoS database. The Conference Proceedings Citation Index--Science (CPCI-S) indexed most papers in the WoS database, totaling 583 publications. Next was the Science Citation Index Expanded (SCI-EXPANDED), with 477 articles published. The Emerging Sources Citation Index (ESCI) indexed the third-highest number of publications (65), but the number of indexed papers already differs by order. This can be explained by the researcher's interest in either making quick publishing in the case of conferences or publishing research in highly ranked journals, which is why ESCI is losing the competition. The number of articles indexed in other indexes is not worth mentioning because of extremely low numbers. Figure 10: Web of Science trend from 1124 OT security publications from the Web of Science database.