@book { ManagementinkommerziellenSportstudios,
    title = "Management in kommerziellen Sportstudios",
    author = "Sebastian {Kaiser}",
    year = "2005",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832443818",
    url = "https://m.diplom.de/document/219991"
}