@book { DerMultiChannelCustomer,
    title = "Der Multi Channel Customer",
    subtitle = "Stand der Forschung",
    author = "Sven {Müller}",
    year = "2009",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783836626804",
    url = "https://m.diplom.de/document/226610"
}