@book { DieELearningUmgebunglearncom,
    title = "Die E-Learning Umgebung learncom",
    author = "Daniel {Backhausen}",
    year = "2005",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832440725",
    url = "https://m.diplom.de/document/219701"
}