The SKOS Mapping RDF Vocabulary has been moved to the w3.org namespace.
The new namespace for SKOS Mapping is:
http://www.w3.org/2004/02/skos/mapping#
The HTTP link for the source RDF is:
http://www.w3.org/2004/02/skos/mapping.rdf
This is now the permanent home for SKOS Mapping. Apologies for any
inconvenience caused.