@book { KundenorientierungimSportverein,
    title = "Kundenorientierung im Sportverein",
    author = "Heiko {Zyder}",
    year = "2005",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832485658",
    url = "https://m.diplom.de/document/223763"
}