@book { WasdiePDLwirklichbraucht,
    title = "Was die PDL wirklich braucht",
    author = "Birger {Schlürmann}",
    year = "2021",
    publisher = "Schlütersche Verlagsgesellschaft mbH & Co. KG",
    address = ", Deutschland",
    url = "https://schluetersche.openpublishing.com/document/993676"
}