Relationships between different XML applications

One important feature that I would like to see in the next version of HTML would be to cover relationships between different XML applications.
I have not seen this addressed in any of the work the W3C is looking at (if I am mistaken on this, please let me know)

I have a detailed article on this at
http://www.inet2001.com/post/Features/Relationships/relationships.html

By adding relationships between, FormML, TableML and MathML, we could have a good spreadsheet application.

I visualize that relationships are something that the XML schema (XML-Data ?) would need to support. Please ignore the syntax, I have used in the article.

This is a very useful feature and will make sure that TableML can use FormML, instead of having it's own edit/input tag.

Comments ?

Thanks,
Ashvil