Schema from DTD how to create docType references

I need to modify an existing DTD to generate the desired resultant schema within webMethods6 Developer.
The current DTD creates a root structure with sub-components but these sub-components are “hard” links instead of “references”.

I’ve had a look at both the Developer User’s Guide and the Schema Reference Guide but have been unable to modify the DTD to create references. How does one distinguish in the DTD between a entry
“<!element>” that creates a hard link X and one that creates
a X (docType_X) ?

Anytime a DTD/XSD element is referenced from more than one place, it is factored out and created as it’s own record/document with references from each corresponding parent element’s record/document.