Validating with a DTD

Validating an XML document requires an XML parser.  Let's use Internet
Explorer to validate against our external DTD.

As you can see since the XML document is linked to a local file that
Internet Explorer can find the XML is validated.

However, if we were to use the same document in an online validator such
as the one created by Brown University's Scholarly Technology Group
errors would occur.

In this case the errors in validation result from the fact that the DTD
file is referenced locally.

Because the DTD is referenced locally when the online validator goes to
look for the DTD it can't find it.  Therefore we can fix this in either
two ways, either we can give the DTD: referenced externally in this case
message.dtd a full url like
http://www.ischool.utexas.edu/technology/tutorials/webdev/xml_dtds/
message.dtd

or we can change and replace the external DTD with an internal one and
revalidate with the online DTD.

In this case let's use the internal dtd option.  As you can see by the
lack or errors the validator doesn't need to look elsewhere for the DTD
to validate against because we've included it internally.

So in this case it able to completely check the document and determine
that it is a valid and well-formed XML document.

Now you know how to create an XML document that will be well-formed and
then also create a DTD that will allow you to validate that XML
document.

Now that you have these skills go out have fun making and creating XML
documents and DTDs.