@book { DiebetrieblicheAltersvorsorgeimMittelstand,
    title = "Die betriebliche Altersvorsorge im Mittelstand",
    author = "Marion {Giesa}",
    year = "2004",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832482695",
    url = "https://m.diplom.de/document/223467"
}