There is a workaround that I have used in the past if you know what your
PUBLIC identier is at resolution time, by throwing an exception. Here is
the example I ran into when using a DTD for RSS 0.91 validation. You can
get this DTD from the URL below.

I had a DTD file that contained PublicId of "-//Netscape
Communications//DTD RSS 0.91//EN"  which is *not* resolvable and local copy
of the same DTD with the SystemId of "c:\samplefiles\rss-0.91.dtd" which
can be resolved. e.g.

<!DOCTYPE rss PUBLIC "-//Netscape Communications//DTD RSS 0.91//EN"  
"c:\samplefiles\rss-0.91.dtd">

In the the GetEntity method you cannot tell when the SystemId is being
resolved as opposed to the PublicId. Hence you have to look at the supplied
string
and throw an exception to force PublicID not be passed to the GetEntity()
method, which is then called again to resolve the SYSTEMID.

So the (unfortunate) workaround is to throw an exception when resolving a
known PUBLICID e.g.

public override Uri ResolveUri(Uri baseUri, String relativeUri)
    {
        // check the PublicID value of the DTD and do not resolve
        // Throwing exception causes the SystemID to be resolved instead
        if (relativeUri == "-//Netscape Communications//DTD RSS 0.91//EN")
            throw new XmlException(" Do not resolved PublicID for -//Netscape
Communications//DTD RSS
0.91//EN", null);

Hope this helps.

Mark Fussell
Program Manager - System.Xml

This posting is provided "AS IS" with no warranties, and confers no rights.

OK, thank you for the information.

In my current situation the only reason for reading the DTD and entities is,
that XML loading does not work when a document contains entity references
that cannot be resolved. If would be sufficient if the framework produced
"EntityReference" nodes in the loaded "XmlDocument".

Any way to work around this restriction?

Regards,
erwin