1. Feller, J., Fitzgerald, B.: Understanding Open Source Software Development. Addison-Wesley, Reading (2002)
2. Munga, N., Fogwill, T., Williams, Q.: The adoption of open source software in business models: A Red Hat and IBM case study. In: Annual Research Conference of the South African Institute of Computer Scientists and Information Technologists, pp. 112–121 (2009)
3. Höst, M., Oručević-Alagić, A.: A systematic review of research on open source software in commercial software product development. In: Proceedings of Evaluation and Assessment in Software Engineering, EASE (2010)
4. Robson, C.: Real World Reserach, 2nd edn. Blackwell Publishing, Malden (2002)
5. Kontio, J., Bragge, J., Lehtola, L.: The focus group method as an empirical tool in software engineering. In: Shull, F., Singer, J., Sjøberg, D.I.K. (eds.) Guide to Advanced Empirical Software Engineering, Springer, Heidelberg (2008)