- From: Pat Hayes <phayes@ihmc.us>
- Date: Mon, 4 Oct 2010 13:55:45 -0500
- To: nathan@webr3.org
- Cc: Melvin Carvalho <melvincarvalho@gmail.com>, Semantic Web <semantic-web@w3.org>
On Oct 4, 2010, at 7:33 AM, Nathan wrote: > Pat Hayes wrote: >> Well, the very idea of a *blank* node is one that has no name, so this idea seems to be rather against the spirit of the bnode, so to speak. Of course, concrete syntaxes do use bnode identifiers, but these are really just an artifact of the need to represent a graph in a linear character sequence. These bnode identifiers are purely local to the graph. > > Hmm, does this mean then that often people are using blank nodes as if they have a name, and should this be avoided? > > for example: > > _:x1 rdf:type ex:Person ; rdfs:label "Nathan"@en . > :Bob :knows _:x1 . > :Sue :knows _:x1 . > > as far as I know many RDF processors (and indeed common understanding) would treat this as if to say that: "The person that Bob knows called Nathan is the same person that Sue knows called Nathan" Right, that is correct. > > When it appears that correct interpretation would be "Bob knows a person call Nathan and Sue knows a person called Nathan" No, because those three triples share a single bnode. Draw the actual RDF graph and this will be clear. > > Thus, am I mistaken, or would it be preferably to write: > > _:x1 rdf:type ex:Person ; rdfs:label "Nathan"@en . > :Bob :knows _:x1 . > _:x2 rdf:type ex:Person ; rdfs:label "Nathan"@en . > :Sue :knows _:x2 . > > or even: > > :Bob :knows [ a ex:Person, rdfs:label "Nathan" ] > :Sue :knows [ a ex:Person, rdfs:label "Nathan" ] > > And in the case where the person they know is the same person called Nathan, then to give that person a proper name, a URI reference. > > I guess, more tersely, should a blank node reference '_:' ever appear more than once in the object position of a triple? Yes, sure. > and if it does should parsers create a graph which links both subjects to the same blank node, or produce two different ones? The same, when these triples are in the same graph, of course. Pat > > Best, > > Nathan > > ------------------------------------------------------------ IHMC (850)434 8903 or (650)494 3973 40 South Alcaniz St. (850)202 4416 office Pensacola (850)202 4440 fax FL 32502 (850)291 0667 mobile phayesAT-SIGNihmc.us http://www.ihmc.us/users/phayes
Received on Monday, 4 October 2010 18:56:27 UTC