@book { ProduktundServicemanagement,
    title = "Produkt- und Servicemanagement",
    author = "Manfred {Bruhn} and Karsten {Hadwich}",
    year = "2017",
    publisher = "Vahlen",
    address = "München, Deutschland",
    url = "https://vahlen.openpublishing.com/document/1220838"
}