# Systematic Literature Review of System Models for Technical System Development
## 2 Materials and Methods  
The systematic literature review has been carried out without a systemic review protocol. The study focused on international definition and thus on titles in English. Due to the native language of the authors being German, literature written in German has been declared as eligible as well with the term 'Systemmodell' being equivalent to the English term'system model'. To get a full overview of any possible definition of the term'system model' the year of publication has not been limited in any form. The eligibility has mainly been based on the reference to engineered systems and a possible correlation to MBSE. The scanning period is dated from 18 July 2020 to 31 July 2020. Information sources included the databases Scopus by Elsevier (www.scopus.com (accessed on 21 July 2021)), Web of Science by Clarivate (apps.webofknowledge.com (accessed on 28 July 2021)), SAGE Journals by SAGE Publications (journals.sagepub.com (accessed on 22 July 2021)), IEEExplore of the Institute of Electrical and Electronics Engineers (IEEE) (ieeexplore.ieee.org (accessed on 24 July 2021)) and arXiv.org made available by the Cornell University (arxiv.org (accessed on 31 July 2021)). As of 18 November, Scopus includes 41462 journals, proceedings, books and trade publications ([[https://www.scopus.com/sources.uri](https://www.scopus.com/sources.uri)]([https://www.scopus.com/sources.uri](https://www.scopus.com/sources.uri)) (accessed on 18 November 2021)) from 1960-2020. Web of Science covers 21,419 books, proceedings and journals from 1900-2020 ([[https://clarivate.libguides.com/webofscienceplatform/coverage](https://clarivate.libguides.com/webofscienceplatform/coverage)]([https://clarivate.libguides.com/webofscienceplatform/coverage](https://clarivate.libguides.com/webofscienceplatform/coverage)) (accessed on 18 November 2021)). IEEExplore includes 5,329,188 articles from journals, conferences, early access publications, standards, magazines, courses and books. The date coverage goes from 1872-2021. Sage Journals dates back from 1847-2021 and accesses 1211 journals. arXiv.org covers 1795706 open-access articles explicitly submitted to arXiv.org with a date coverage of 1991-2020. Table 1 summarizes this information and gives an overview of the content of the database. \begin{table}
\begin{tabular}{c c c c} \hline
**Source Name** & **Date Coverage** & **Last Searched** & **Comments on Included Data** \\ \hline Scopus & 1960–2020 & 21 July 2020 & 41,462 journals, proceedings, trade publications and books \\ Web of Science & 1970–2020 & 28 July 2020 & 21,419 books, proceedings and journals \\ Sage Journals & 1847–2020 & 22 July 2020 & 1211 journals \\ IEEExplore & 1872–2021 & 24 July 2020 & 5,329,188 articles from journals, conferences, early access publications, standards, magazines, courses and books \\ arXiv.org & 1991–2020 & 31 July 2020 & 1,795,706 open-access articles (only explicitly submitted to arXiv.org) \\ \hline \end{tabular}
\end{table} 
Table 1: Overview of information sources. No additional sources have been used. As the search for the term'system model' would bring too many results regarding different kinds of non-technical systems and models in various contents, the keywords have been refined. The following keywords have been used:  
1. federated system model
2. system model creation
3. system model development
4. system model usage
5. system model fidelity
6. system model complexity
7. system model uncertainty
8. multi-model networks
9. model hierarchy
10. system model perspectives
11. system model visualization
12. system model characteristics
13. transdisciplinary system model
14. interdisciplinary system model
15. system model + MBSE
16. system of systems model  
The search for these keyword-searches has been carried out as demonstrated in the following for the Scopus database:  
1. The advanced search of the database has been located and the keywords were entered for searching the title, abstract and keywords, if available.