@book { Projektentwicklungnachdem4PhasenModell,
    title = "Projektentwicklung nach dem 4-Phasen-Modell",
    author = "Stephanie {Ullmann}",
    year = "2007",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783836602976",
    url = "https://m.diplom.de/document/228842"
}