Problem with Cyclic DTD's

[Sanjay Mishra]

Hello,
I am writing a visual tool to write xml file based upon the dtd
file. The user will load the dtd file, elements and attributes
will be shown in a tree form. The user will select the elements/attributes and xml file will be generated.
Here, I have no idea how to deal with the cyclic dtd's. Like:
<!ELEMENT A (B)*>
<!ATTLIST A name CDATA #IMPLIED>
<!ELEMENT B (A|X|Y)>
<!ELEMENT X (#PCDATA)>
<!ELEMENT Y (#PCDATA)>
Please help me.
Regards
Sanjay.