@book { OperativesControllingingastgewerblichenKleinundMittelbetrieben,
    title = "Operatives Controlling in gastgewerblichen Klein- und Mittelbetrieben",
    author = "Wolfgang {Kernbeis}",
    year = "2006",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    url = "https://m.diplom.de/document/224814"
}