hi hari,
i don't think your application search for PUBLIC dtd. Isn't it just unique namespace differentiate the namespace amongst various name sources?
you could find out the DTD in that site, but even though they don't provide it, it wouldn matter to validate your xml file. For example, when you make a client application to connect the Server (in this case SUN),
you should follows their DTD as they provided to match the name and type. In this case, you can differentiate your namespace and theirs. It they don't have specific DTD file, they should provide xml file has a DTD information or just DTD to work your application.
correct me if i am wrong.