@book { BusinessplanTheoreticalGuide,
    title = "Businessplan - Theoretical Guide",
    author = "Daniel {Gschwend}",
    year = "2004",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832480493",
    url = "https://m.diplom.de/document/223282"
}