- ITC, page 1000-1005. IEEE Computer Society, (1990)
- ITC, page 665-668. IEEE Computer Society, (1988)
- Encyclopedia of Complexity and Systems Science, Springer, (2009)
- IDC, volume 78 of Studies in Computational Intelligence, page 155-164. Springer, (2007)
- International Journal of Geographical Information Science 25(10):1561-1574 (2011)
- J. Digit. Inf. (2011)
- J. Location Based Services 5(1):3-21 (2011)
- Oldenbourg Wissenschaftsverlag, (July 2002)
- EWSN, page 158-165. IEEE, (2005)
- Journal of Economic Surveys 14(5):527-561 (2000)
- Expert Syst. Appl. 37(12):7509-7520 (2010)
- Intelligente Systeme zur Entscheidungsunterstützung, page 205-220. SCS Publishing House e.V., (2008)
- EC-TEL, volume 6383 of Lecture Notes in Computer Science, page 420-425. Springer, (2010)
- Bild der Wissenschaft (7):94-97 (2010)
- Bild der Wissenschaft (4):68-69 (2010)mit Lit.-Hinweis .
- Bild der Wissenschaft (4):60-67 (2010)mit Lit.-Hinweisen und Internetadressen .
- Journal of Business Venturing 5(1):15--28 (1990)
- Journal of Business Venturing 10(3):371--391 (1995)
- J. Location Based Services 1(1):5-45 (2007)
- J. Location Based Services 1(2):89-111 (2007)


author