@book { DirektmarketingfrFacilityManagementUnternehmen,
    title = "Direktmarketing für Facility-Management-Unternehmen",
    author = "Sven {Klingelhöfer}",
    year = "2007",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783836604536",
    url = "https://m.diplom.de/document/228957"
}