@book { WeiterbildungsmarketingfrdieZielgruppe50plus,
    title = "Weiterbildungsmarketing für die Zielgruppe 50plus",
    author = "Jürgen {Nill}",
    year = "2011",
    publisher = "Diplom.de",
    address = "Hamburg, Germany",
    doi = "10.3239/9783842814615",
    url = "https://m.diplom.de/document/228499"
}