Are duplicate property/value pairs permitted for a resource?

If an RDF processor is asked to add a property/value pair for a resource,
but that property/value pair already exists for that resource, should the
processor:

(a) Add a duplicate property/value pair to the resource, or
(b) Ignore the "new" property/value pair?

I couldn't find anything in the spec regarding this issue.  The closest
thing I found had to do with fact that the Bag and Seq containers allow
multiple instances of the same value.  However, that isn't even the same
issue, since items within a collection have unique property names (rdf:_1,
rdf:_2, etc.)

Samuel C. Yang
syang@peoplemoverinc.com
 <<Samuel C. Yang.vcf>>