@book { Stadtmarketing,
    title = "Stadtmarketing",
    author = "Birgit J. D. {Flake}",
    year = "2007",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783836603898",
    url = "https://m.diplom.de/document/228921"
}