@book { Projektmanagement,
    title = "Projektmanagement",
    subtitle = "Wissensbausteine für die erfolgreiche Projektarbeit",
    author = "Michael {Hesseler}",
    year = "2015",
    publisher = "Vahlen",
    address = "München, Deutschland",
    url = "https://vahlen.openpublishing.com/document/1220809"
}