Some RDQL questions

Hi,

I'm currently working on the (RDBMS based) storage backend of an OWL based 
knowledge/content management system. So I'm looking around what components 
are already there. I have come across RDQL but didn't find much in terms of 
documentation. I have looked at the BNF and the jena tutorial but some 
questions remain:

* Is there any way to specify ordering like with the SQL order by clause?

* Am I right to assume that there is no support for aggregate functions?

* Would it be possible to query for all resources that do not have a 
certain property?

* If I think of a TriplePatternClause in terms of SQL joins, does it have 
inner or outer join semantics? For example if I say:


SELECT ?lastname, ?email
WHERE
         (?r, <my:lastname>, ?lastname) ,
         (?r, <my:email>, ?email)

Will the lastname of ?r be included in the result set even if it has no 
email address? Can I change this behaviour whichever it may be?

* Does RDQL mandate anything with respect to inference along 
subPropertyOf/subClassOf lines or is this considered an implementation detail?

Thanks in advance,

-Alexander