@book { PersonalServiceAgenturen,
    title = "Personal Service Agenturen",
    author = "Heike {Eekhoff}",
    year = "2004",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832481391",
    url = "https://m.diplom.de/document/223363"
}