@book { StrategischeGruppeninderMedienbranche,
    title = "Strategische Gruppen in der Medienbranche",
    author = "Gorden {Dubbels}",
    year = "2003",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832465919",
    url = "https://m.diplom.de/document/221982"
}