how should undefined elements figure in aggregate samples?

good evening,

should the sparql aggregation mechanism exclude unbound elements from the aggregation set?
must it?
may it?

in order for a query to correlate elements from sparse graphs, it seems that the unbound elements should be excluded.
still, i wonder what the recommendation intended.
there appears to be no directly relevant test in the w3c suite and while the language in the recommendation permits the more useful result, it leaves open the consequences, should the respective value set include undef markers only.

to be specific, is there a canonical result for the following query?

select ?o
        (sample(?s) as ?sSample)
        (count(?s) as ?sCount)
     	(sample(?p) as ?pSample)
     	(count(?p) as ?pCount)
     	(sum(?v) as ?vSum)
where {
 values (?s ?p ?o ?v)
 { (<http://example.org/s1> undef <http://example.org/o1> undef)
   (<http://example.org/s2> undef <http://example.org/o1> 1)
   (<http://example.org/s3> undef <http://example.org/o1> undef)
   (<http://example.org/s4> <http://example.org/p4> <http://example.org/o1> 1)
   (<http://example.org/s5> undef <http://example.org/o2> undef)
   (<http://example.org/s6> undef <http://example.org/o2> 1)
   (<http://example.org/s7> <http://example.org/p6> <http://example.org/o3> 1)
   (<http://example.org/s8> undef <http://example.org/o3> 1)
 }
} group by ?o



best regards, from berlin,
---
james anderson | james@dydra.com | http://dydra.com