Google docs queuing system using UML class diagrams

How to represent a system like google docs queuing system using UML class diagrams? I haven't used much UML and trying to design a system like Google docs.

Solution

I'm not a UML pro but I took a quick stab at it. There's probably some missing pieces here but I think it's a good start. It would be great if someone who knows how to correctly model this can provide their diagram.