- From: Bijan Parsia <bparsia@cs.man.ac.uk>
- Date: Wed, 6 Sep 2006 12:19:51 +0100
- To: RDF Data Access Working Group <public-rdf-dawg@w3.org>
http://www.w3.org/2001/sw/DataAccess/issues#formsOfDistinct I believe some members of the working group believe that this cannot be settled without advances on the core semantics. I think, however, we can make some progress and perhaps decide on somethings we *don't* want. So, it is clear to everyone, I hope, that there are several possible sense of DISTINCT. For a simple set of examples, see: <http://www.cs.man.ac.uk/~bparsia/2006/row-tutorial/slide#35> (and the subsequent 2) (Now the exact effect of these different senses will partially depend on the BNode scope: <http://www.cs.man.ac.uk/~bparsia/2006/row-tutorial/slide#27> and subsequent For example, pairwise subsumption only makes sense, IMHO, if we have answer level scoping in answers. That is, bnodes in answers only corefer *within* an answer, not between answers. There it makes a *lot* of sense.) So, the high level point is whether we want to support 2 forms of DISTINCT or only one. This has the effect of having three levels of redundancy, e.g.,: The normal case DISTINCT REALLYREALLYDISTINCT (I hope these will nest. I *think* source lean answers are always a superset of answer lean answers, but I've not shown it.) Since I don't believe the group will endorse answer scope, then I believe there are only two senses of distinct at play. Source lean and answer set lean. Pat and Andy have championed some form of Source leanness. I've championed answer set leanness. I think the group has enough information right now to decide whether they have one or two forms of DISTINCT, and if one, which one. If we decide on two, we need to add a keyword or other way of indicating which sense of distinct is in play. If only one, we can defer which one for a while if the group would like to gather more information. Oh, this only settles BNode redundancy. We still need to be clear on literal and blank redundancy. I'm happy to provide more examples, clarifications, etc. Cheers, Bijan.
Received on Wednesday, 6 September 2006 11:20:08 UTC