Using Xml in Visio 2003 UML

I want to use Xml in order to create and modify the UML Template shapes the
Visio's Model Explorer -
basically creating some sort of pool from which I'll take the shapes that I
want and the connections between the shapes will be instored already in them
.
(the basic idea is having some sort of DB of shapes that can be modified out
side from the Visio and when I get it inside the visio the changes of the cl
asses for example with the connections between them are shoed in the drawing
s)

do you have any suggestions on how can I do that?

thanks,
IR