@book { LeitfadenzurEntwicklungeinerECStrategie,
    title = "Leitfaden zur Entwicklung einer EC-Strategie",
    author = "Mathias {Bretzger}",
    year = "2001",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832447243",
    url = "https://m.diplom.de/document/220326"
}