1. Brindley, J. E., Wälti, C., & Zawacki-Richter, O. (2004). The current context of learner support in open, distance and online learning. In J. E. Brindley, C. Wälti, & O. Zawacki-Richter (Eds.), Learner support in open, online and distance learning environments (pp. 9–27). Oldenburg: Bibliotheks- und Informationssystem der Universität Oldenburg.
2. Delling, R. M. (1971). Grundzüge einer Wissenschaft vom Fernstudium. Epistolodidaktika, 1, 14–28.
3. Garrison, G. R. (1985). Three generations of technological innovation in distance education. Distance Education, 6(2), 235–241.
4. Garrison, D. R., Anderson, T., & Archer, W. (2000). Critical inquiry in a text-based environment: Computer conferencing in higher education. The Internet and Higher Education, 2(2–3), 87–105.
5. Holmberg, B. (1986). Growth and structure of distance education. Beckenham: Croom Helm.