@book { KlassifikationvonPortalundCommunitySites,
    title = "Klassifikation von Portal und Community Sites",
    author = "Michael {Abbate}",
    year = "1999",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832419233",
    url = "https://m.diplom.de/document/217771"
}