Updating WPF GUI from a DLL

Question

This seems like it would be pretty common task, but I'm not having any luck searching for an answer.

I have a WPF/C# application that relies heavily on a dll for database routines. I would like the dll to update some GUI elements, i.e. a progress bar.

So far, it seems that the answer lies somewhere in System.ComponentModel and creating a backgroundworker. But that's as far as I can get.

Can someone please offer suggestions on how to accomplish this task? Links, sample code, encouraging words appreciated!

Many thanks,

Jerry