# Some fields, like Cc and Bcc, are often empty: this means that most
# of the times you query for "?message email:cc ?cc" you will have 
# very few results. This is the reason why fields like this have to 
# be kept OPTIONAL (try the difference taking away the OPTIONAL clauses 
# from the query).

PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>
prefix email: <http://davide.eynard.it/rdf/email#>

select * where
{
	?x email:subject 	?subject .
	?x email:from		?from .
	?x email:to 		?to .
	OPTIONAL{	?x email:cc 		?cc }. # note: this should normally be left as optional
	OPTIONAL{	?x email:bcc 		?bcc }. # note: this should normally be left as optional
}