@phdthesis{Gruene2008,
  author      = {Markus Gr{\"u}ne},
  title       = {Flexible Abrechnungssysteme f{\"u}r digitale Produkte im E-Learning},
  type        = {doctoralthesis},
  school      = {Universit{\"a}tsbibliothek Johann Christian Senckenberg},
  year        = {2008},
}