Can I resolve the URI used as an XML namespace name?
12.4) Can I resolve the URI used as an XML namespace name?
Yes.
You can also eat a tractor, but that doesn’t mean it’s a good idea.
What I love most, also from the same FAQ is this:
Furthermore, there is nothing in the processing of XML namespaces that requires you to resolve these URIs. Finally, as was noted in the previous question, many types of namespace URIs are unresolvable on the Web.
I don’t know how many developer’s have wasted hours because of a second parameter in their API that accepts an XSD and a URI:
The schema specification correctly recognizes the lack of robustness due to xsi:schemaLocation. According to the specification, xsi:schemaLocation is only a hint to the parser and the parser may use other means to decide which schema to apply.