@book { MakeorbuydesRechnungswesensinKMU,
    title = "Make-or-buy des Rechnungswesens in KMU",
    author = "Markus {Kempmann}",
    year = "2005",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832488161",
    url = "https://m.diplom.de/document/223996"
}