abstract model and reification

A colleague has pointed this out to me, from m&s:

  When a resource represents a reified statement;
  that is, it has an RDF:type property with a 
  value of RDF:Statement, then that resource 
  must have exactly one RDF:subject property,
  one RDF:object property, and one RDF:predicate
  property.

Oh well ...

Brian McBride
HPLabs