@book { OnlineMarktforschunginderTourismuswirtschaft,
    title = "Online-Marktforschung in der Tourismuswirtschaft",
    author = "Karin {Robles Sy}",
    year = "2003",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832470036",
    url = "https://m.diplom.de/document/222313"
}