@book { IncreasingCustomerLoyaltyviaMobileCustomerRelationshipManagement,
    title = "Increasing Customer Loyalty via Mobile Customer Relationship Management",
    author = "Silke {Freitag}",
    year = "2002",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832456894",
    url = "https://m.diplom.de/document/221163"
}