@book { VirtuelleCommunities,
    title = "Virtuelle Communities",
    author = "Kirsten {Lenz}",
    year = "2001",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832446581",
    url = "https://m.diplom.de/document/220267"
}