- From: Pat Hayes <phayes@ihmc.us>
- Date: Tue, 29 May 2007 14:12:32 -0700
- To: Bob MacGregor <bmacgregor@siderean.com>
- Cc: public-rdf-dawg-comments@w3.org, "Eric Prud'hommeaux" <eric@w3.org>, "Richard Newman" <rnewman@franz.com>
>Hi Richard, > >On May 28, 2007, at 1435, Richard Newman wrote: > >>Hi Bob, >> >><snip> >> >> Regarding point 2: yes, AllegroGraph allows you to store whatever >>you like in the graph field of a triple. Other stores might not. >>I'm not sure that I agree with you about naming -- why not mint >>URIs, or use UUID URNs? You can cram almost anything into a URI! -- >>but you can certainly use variables in your queries. >> > >The phrase "mint URIs" raises a red flag, since it is frequently >contrary to the whole point of a URI. That is definitely true in >this case. >Suppose I have two graphs with identical triples, and identical >provenance attached to their "graph names". I claim that these >two graphs should be considered equivalent. If the graphs are >identified with blank nodes, then that is indeed the case. >Otherwise, >its not. The presence of a URI overdefines the semantics of the >provenance. Does this matter? Indeed it does. Our quad store >does union and collapsing operations on provenance to increase >performance (sometimes by orders of magnitude). The operations >it performs are not valid if URIs are present. I would not be >surprised if AllegroGraph does not yet incorporate these >optimizations. >However, once you start to use sufficiently aggressive provenance, >its likely you will want to do the same. ?? Bob, what are you talking about? Lets agree for the moment with your claim that the two graphs should be equivalent (though Im having trouble understanding how they can have *identical* provenance information if one is a copy of another; perhaps we mean something different by 'provenance'). You say that if they have different names, they cannot be equivalent. Why not? The entire RDF/URI model allows a single entity to have more than one name. The point of URIs is to identify, but not to identify uniquely. So in fact the two graphs can be identical, if you like, like two imprints of the same edition of a novel. Why are your optimizing collapsings not valid if URIs are present? You can simply declare that your identity criteria on graphs allow a graph (not a named graph, but an RDF graph) to have more than one name without being a different graph. You are free to impose extra semantics on the basic RDF model if you find it useful. Nothing in RDF or SPARQL suggests that different names cannot denote the same thing. A further puzzle is that you are happy if the name is a blank node... do I have that right? That simply does not make sense to me. Blank nodes cannot be used as names or identifiers. The meaning of a blank node is to express an existential assertion. Using a blank node as an identifier is meaningless. 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 Tuesday, 29 May 2007 21:12:39 UTC