Connecting elements using lines/paths

Hi,

I am looking at using SVG as a modelling language for ontologies, UML, RDBMS
etc. There, in my point of view, seems to be a feature missing in the current
specification. Is it possible to define two elements, like two rectangulars,
and then define a line or a path connecting them. This way it would be
possible to change one of the rectangulars without having to redefine the
coordinates for the line/path. This could perhaps be done by specifying the
end coordinates for the line as a reference to a point within the
rectangulars. Maybe one could define "connection points" for every shape in
SVG?

Has anyone thought of this or is it outside the goal of SVG?

regards,
Erik Hellman