@book { SystematischesOutsourcingdesFacilityManagement,
    title = "Systematisches Outsourcing des Facility Management",
    author = "Gerfried {Walser}",
    year = "2003",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832464073",
    url = "https://m.diplom.de/document/221834"
}