@book { OnlineServiceCenter,
    title = "Online Service Center",
    subtitle = "Die Integration von Internet und Call Center als Instrument zur Kundenbindung im Rahmen des Relationship Marketing",
    author = "Markus {Wierl}",
    year = "1998",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832410476",
    url = "https://m.diplom.de/document/216939"
}