@book { VirtualCommunitiesimInternet,
    title = "Virtual Communities im Internet",
    author = "Martin {Kranwetvogel}",
    year = "1999",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832415273",
    url = "https://m.diplom.de/document/217372"
}