DAML+OIL for Application Developers - slide "XML Namespaces"

RDF(S) and DAML+OIL use Qualified Names (QNames) from the XML Namespaces Recommendation to abbreviate URIs
- e.g. rdf:type might expand to http://www.w3.org/1999/02/22-rdf-syntax-ns#type

a namespace prefix is defined within the scope of an element containing xmlns attributes, e.g.


<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
         xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#">
  <rdfs:Class rdf:ID="Foo"/>
  ...
</rdf:RDF>

a default namespace can optionally be defined using xmlns without a prefix, e.g. the following is equivalent to the example above


<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
         xmlns="http://www.w3.org/2000/01/rdf-schema#">
  <Class rdf:ID="Foo"/>
  ...
</rdf:RDF>

in RDF(S), QNames can be used as XML element tags and attributes names, but not within attribute values, e.g.


<!-- BAD: -->
  <rdfs:subClassOf rdf:resource="rdfs:Resource">
<!-- GOOD: -->
  <rdfs:subClassOf rdf:resource="http://www.w3.org/2000/01/rdf-schema#Resource">
<!-- GOOD: -->
  <!DOCTYPE rdf:RDF [
    <!ENTITY rdfs 'http://www.w3.org/2000/01/rdf-schema#'>
  ]>
  ...
  <rdfs:subClassOf rdf:resource="&rfds;Resource">