Defining Action (rowset type) in SSAS

Hi
I need to build an Action on a measure that belongs to a cube that behaves like a DrillThrough Action that returns details related to a measure.
The problem is that the details data should come from a table that is not inside the cube but it is in an SQLServer relational DB.
So, it is possible to define an Action that could retrieve data from an external DB?
If so, For this action i chose target type as 'cells', target object as 'all cells' and action type as 'rowset' for returning tabular form. But I have to make this action to work on 3 dimension, how I'll write the Action expression ?? this is where I am stuck at.
Really appreciate the help.
Thank you.

Hello !
did you receive any answer to your post ?
i now have the same problem, I try to access details from my database (outside the cube), but I don't know the syntaxis to full 'Action expression' !
I would really appreciate your help !
thank's

Thanks for your answer, but unfortunately I've allready read those documents and didn't find the answer to my question.
Thanks again !
Fred