@book { ExternesundInternesRatingimVergleich,
    title = "Externes und Internes Rating im Vergleich",
    author = "Michael {Guggenberger}",
    year = "2015",
    publisher = "BACHELOR + MASTER PUBLISHING",
    address = "Hamburg, Deutschland",
    url = "https://m.bachelor-master-publishing.de/document/308973"
}