@book { BetrieblicheUmweltinformationssysteme,
    title = "Betriebliche Umweltinformationssysteme",
    author = "Wilhelm {Heckmann}",
    year = "2002",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832451172",
    url = "https://m.diplom.de/document/220644"
}