# something along the lines

SELECT ?common_documents WHERE  #distinct might be needed
{	 
	SELECT ?document
WHERE {
	GRAPH prj:disease_gene_microbe_small {
			?denotation tao:denoted_by ?span ; a __ENTITY1__ .
      	#e.g. __ENTITY2__ : http://disease- 
#              ontology.org/term/DOID:0060192
	}
#?span tao:belongs_to ?document . #NOT WORKING, somehow the project #is not being RDF-ized properly
}
UNION
{
SELECT ?document
WHERE {
	GRAPH prj:disease_gene_microbe_small {
			?denotation tao:denoted_by ?span ; a __ENTITY2__ .
      	#e.g. __ENTITY2__ : http://pubannotation.org/projects/disease_gene_microbe_small/stringdb:9606.ENSP00000300589
	}
#?span tao:belongs_to ?document . #NOT WORKING, somehow the project #is not being RDF-ized properly
}