Has anyone found good documentation and/or examples on creating Communication Type System Extracts?

I wasn't sure if this was the proper sub-space, but since System Extract tool started as a Benefits function I thought I'd try.

Has anyone found any articles that explain how to create communication type extracts?  Especially being able to dynamically determine who should receive them as an email (i.e. specific supervisors as of that date for example)?  I am trying to figure it out by playing around but either it isn't capable of doing much or I'm just missing something.

Any help would be appreciated!

Thanks,

Jim