Named graphs

[Laura Morales]

If I've read the W3 standards correctly, labels for graphs must be IRIs. Jena 
also seems to enforce this behaviour, as it throws an exception if I use a 
literal. My question is, why is this enforced at all? Why can't I name my 
graphs with literals, for example "graph-1" or "graph-2"?
And related to this question, is there anything wrong (in any way) if I'm going 
to name my graphs <graph-1>, <graph-2>, etc. (basically the same name, but with 
IRI notation instead of literals)?