@book { TheCoachontheLeisureTravelMarket,
    title = "The Coach on the Leisure Travel Market",
    author = "Martin {Schiefelbusch}",
    year = "1999",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832418113",
    url = "https://m.diplom.de/document/217666"
}