@book { InformellesLernen,
    title = "Informelles Lernen",
    subtitle = "Ein Überblick",
    author = "Sebastian {Wurm}",
    year = "2007",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783836603355",
    url = "https://m.diplom.de/document/228906"
}