@book { BusinessplanfreinIngenieurbro,
    title = "Businessplan für ein Ingenieurbüro",
    author = "Michael {Daschner}",
    year = "2005",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832440619",
    url = "https://m.diplom.de/document/219690"
}