@book { Marketingdutourismedurable,
    title = "Marketing du tourisme durable",
    author = "Susanne {Häcker}",
    year = "1998",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832410629",
    url = "https://m.diplom.de/document/216954"
}