@book { OpenSourceCustomerRelationshipManagementSolutions,
    title = "Open Source Customer Relationship Management Solutions",
    author = "Henrik {Vogt}",
    year = "2008",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783836615921",
    url = "https://m.diplom.de/document/225949"
}