- From: Bijan Parsia <bparsia@cs.man.ac.uk>
- Date: Mon, 21 Aug 2006 11:00:43 +0100
- To: andy.seaborne@hp.com
- 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. > (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. Cheers, Bijan.
Received on Monday, 21 August 2006 10:00:55 UTC