@book { KonzeptioneinesCustomerLifetimeValues,
    title = "Konzeption eines Customer Lifetime Values",
    author = "Markus {Grauvogl}",
    year = "2006",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832496654",
    url = "https://m.diplom.de/document/224742"
}