@book { mLearningviaPDA,
    title = "m-Learning via PDA",
    subtitle = "Betrachtung von Technik und Zukunftsperspektiven mobiler Lernumgebungen",
    author = "Michael {Baum}",
    year = "2003",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832471071",
    url = "https://m.diplom.de/document/222425"
}