@book { IntelligentesCouponingamPointofSale,
    title = "Intelligentes Couponing am Point of Sale",
    author = "Burkhard {Friedrichsen}",
    year = "2008",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783836623094",
    url = "https://m.diplom.de/document/226387"
}