@book { AnalyseeinesaktivenBeschwerdemanagementsamBeispielderStadtGeldern,
    title = "Analyse eines aktiven Beschwerdemanagements am Beispiel der Stadt Geldern",
    author = "Markus {Hillmann}",
    year = "2003",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832465032",
    url = "https://m.diplom.de/document/221920"
}