@book { ZielgruppenmarketingderReisebrancheinderGayCommunity,
    title = "Zielgruppenmarketing der Reisebranche in der Gay Community",
    author = "Steffen {Erhardt}",
    year = "2003",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832473099",
    url = "https://m.diplom.de/document/222607"
}