@book { SenioreninderHotelundGaststttenwirtschaft,
    title = "Senioren in der Hotel- und Gaststättenwirtschaft",
    author = "Kerstin {Matthiessen}",
    year = "2007",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783836604949",
    url = "https://m.diplom.de/document/228983"
}