- From: Pat Hayes <phayes@ihmc.us>
- Date: Thu, 24 Aug 2006 09:52:49 -0700
- To: Bijan Parsia <bparsia@cs.man.ac.uk>
- Cc: RDF Data Access Working Group <public-rdf-dawg@w3.org>
>On Aug 21, 2006, at 10:53 AM, Seaborne, Andy wrote: > >>Bijan Parsia wrote: >>>I believe that the qualms Andy had about what happens in >>>intermediate steps was do the different interpretations of what >>>the minimized final answer set would look like. That is, his >>>understanding was close to 1 (like pat) and mine were entirely >>>different. However, algorithms for computing 2 and 3 are easy >>>enough, so I'm doing the action item anyway. >> >>My reservations are: >>0/ BNodes over the graph matter - not answer sets >>1/ Lack of streaming >>2/ Additional processing cost [*] >>3/ Non-standard processing (i.e. can't be, say SQL DISTINCT). > >Thanks for the clarifications. > >>[*] Even assuming you want to do it at all, graphs can be leaned >>once, then queried many times. Answer sets have to be leaned on >>every query result. > >Very true. Though if we deal with updates as many real engines do, >the gap narrows a bit. Also, for many applications (cmd line based >query where you load the file each time) this is not true. Of >course, it is most true where you need the most speed, i.e., servers >with big triples store and lots of queries. OTOH, it's unclear how >painful typical queries will be. A lot depends on the size of the >result set and the amount of redundancy. > >>>So, first qualification: These algorithms are only minimizing with >>>respect to BNodes. You have to plug in your own account of >>>literals. I use "row" for "answer" avoid confusion: >>>DEFINITION 1: Answer graph template >>> Let A be an answer set and Avar be the set of column headings of A. >>> The answer graph template of A is the set of triple patterns, >>>such that: >>> {tp | _:row ('http://var.org/#" ++ var) var. & var \in Avar} >> ^^^ >>value? > >I just needed a random URI prefix. Substitute any you like. We did once consider a proposal to have a special 'anonymous' prefix, basically an IRI space solely for skolem names, as part of the spec. That idea kind of died, I think (?) because it was felt to be artificial and not in the IRI spirit of rock-solid eternal universal identifiers that retain their meaning throughout the known universe, but it might be worth reconsidering it. There are emails about this in the archive somewhere but I confess I can't actually find them now. >>(Just to show I'm reading this all!) > >Heh. > >Oh, if we had (do we have?) CONSTRUCT DISTINCT, I would personally >expect a lean graph as output. I agree, if we have this, but I hope we don't :-) Pat -- --------------------------------------------------------------------- IHMC (850)434 8903 or (650)494 3973 home 40 South Alcaniz St. (850)202 4416 office Pensacola (850)202 4440 fax FL 32502 (850)291 0667 cell phayesAT-SIGNihmc.us http://www.ihmc.us/users/phayes
Received on Thursday, 24 August 2006 16:53:15 UTC