Why doesn't the W3C RDF validator replace the URI using the full namespace?

Question

I tried validating a very simple manually-written RDF online, using the W3C RDF Validator. To my surprise, it correctly resolved the URIs from the rdf namespace, but not from a different namespace (also from W3C). Why did this happen?

Let's take the example of

<?xml version="1.0"?>
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
  xmlns:org="http://www.w3.org/ns/org#" >
  <rdf:Description rdf:about="https://stackexchange.com/">
    <rdf:type rdf:resource="org:Organization"/>
  </rdf:Description>
</rdf:RDF>

This validates, and gets parsed to

As you can see, the predicate (rdf:type) gets nicely expanded, and one can click on it. The object (org:Organization) doesn't get expanded at all, and also when I try clicking the link, it literally sends "org:Organization" to the browser, producing an error. But the namespace org has been defined just like the rdf namespace, and if I manually visit http://www.w3.org/ns/org#Organization, I get a Turtle document.

So, my question is: why doesn't it place http://www.w3.org/ns/org#Organization in the object? What should I change for the parser to do it properly?

Answer 1

The parser is doing it properly, actually. The problem is that you are trying to use an XML namespace prefix inside an attribute value (the value of the rdf:resource attribute), rather than as a qualifier on an actual XML element/attribute name itself (such as rdf:type, which is an XML element name).

Put differently: you can't use XML namespaces inside string values. The parser therefore doesn't try to "expand" the namespace, instead just parses the literal string value as a URI, and since org:Organization is in fact a syntactically legal URI, that's what it produces.

To get your desired output, you will have to write out the full IRI string, like so:

<?xml version="1.0"?>
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
  xmlns:org="http://www.w3.org/ns/org#" >
  <rdf:Description rdf:about="https://stackexchange.com/">
    <rdf:type rdf:resource="http://www.w3.org/ns/org#Organization"/>
  </rdf:Description>
</rdf:RDF>

or if you like, you can use abbreviated RDF/XML syntax, to get this:

<?xml version="1.0"?>
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
  xmlns:org="http://www.w3.org/ns/org#" >
  <org:Organization rdf:about="https://stackexchange.com/" />
</rdf:RDF>

As an aside: RDF/XML is a notoriously tricky syntax to work with. There are other, far easier syntax formats for RDF, like for example Turtle. Just sayin'.