Accessing Visio Database Reverse engineering schemas through an addin

Question

I'm trying to build a visio addin that allows me to get a list of tables when a database reverse engineer is run.

I'm using the Microsoft.Office.Interop.Visio library. I can find a list of shapes on the page, but this gives me every single shape on the page and every single piece of text. i would like to have a list of just the database tables (their physical names) in the document.