@book { CustomerProfitabilityAnalysisToday,
    title = "Customer Profitability Analysis - Today",
    author = "Eileen {Schäfer}",
    year = "1999",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832416355",
    url = "https://m.diplom.de/document/217514"
}