@book { KundenbindungbeimOnlineMarketing,
    title = "Kundenbindung beim Online-Marketing",
    author = "Gellért {Horváth}",
    year = "2009",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783836638814",
    url = "https://m.diplom.de/document/227393"
}