- From: Pat Hayes <phayes@ai.uwf.edu>
- Date: Fri, 12 Oct 2001 14:33:13 -0500
- To: Graham Klyne <GK@NineByNine.org>
- Cc: w3c-rdfcore-wg@w3.org
>[Re-post, with comments to specific issues raised in the original >issue -- see end of this message. I've also re-phrased point 3 to >avoid the phrase "normal use".] > >With respect to the issue: >[1] http://www.w3.org/2000/03/rdf-tracking/#rdfms-identity-anon-resources > >Being a revision of my previous message: >[2] http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2001Aug/0030.html > >And citing the model theory document: >[3] http://www.w3.org/TR/2001/WD-rdf-mt-20010925/ > >I propose the following resolution text: Since it looks like this is back out of the closet, a few minor suggestions on wording: >[[[ >1. Resources that are described but not named in an XML >serialization (by rdf:ID or rdf:about) are represented in an RDF >abstract graph by nodes that do not have any associated URI. Might ruffle fewer feathers if instead of saying 'do not have', say 'are not identified by'. (After all, anything might *have* a URI, right? It says that in the Creed.) The point is that these nodes aren't being identified by their URI in the RDF graph; any URI that they might have is outside their RDF-graph syntactic role and should be invisible to, or be deliberately ignored by, any RDF engine. > Such nodes, called bNodes (from blank nodes) are thereby >distinguishable from other described resource nodes, which do have >an associated URI-reference label. ...which are identified by their URI label. >To directly address the question of the issue: a so-called >anonymous resource has no URI. ...resource is not referred to by a URI in an RDF graph. (OR: ...resource has no URI in the RDF graph.) Actually it might be better to avoid the term 'anonymous resource' altogether. After all, the same resource might be anonymous in one graph but referred to by a URI in some other graph. I don't think we can ever know if a resource is truly anonymous, since someone, somewhere, might have given it a URI without telling us. Suggested re-wording: a so-called anonymous resource is one that is not identified by a URI in the RDF graph being considered. >2. To reflect un-named descriptions in N-triples To refer to blank nodes in an N-triples document >, local names must be >introduced (i.e. of the form '_:name'). These names are not URIs, and >their scope is the N-triples document in which they appear. Right. It is important that these not be general URIs in the N-triples document, since then there would be no way to distinguish them from the URIs intended to be in the graph. Also it might be worth saying explicitly that these local names are not part of the graph itself, but are used only within the N-triples syntax to identify graph nodes. They are just artifacts of the need to describe a graph in a linear lexical form. They really aren't part of RDF at all, so this isn't creeping terminology-rot. >3. In the defined use of RDF to express ground facts, the meaning of >bNode is to assert the existence of at least one resource which is >the subject and/or object of properties as indicated by the graph. >This is covered more formally by the Model Theory [3], section 2. >See also the anonymity lemmas in section 3.2. Sorry to bring up yet another terminological quibble, but this term 'bNode' is rather unfortunate. It would be better to call them something like 'nodeID', to emphasize that this thingie in the N-triples syntax really is the name *of a node*, rather than an label attached to the node in the graph. The problem with 'bNode' is that it reads as though the thing in the Ntriplesdoc actually is the blank node itself; we often talk to one another using 'bNode' as a synonym for 'blank node', in spite of it really being a syntax class name in N-triples, which is a bit like waiters referring to a customer by mentioning the food he is eating. It is perilously easy to read this as meaning that the node in the RDF graph has a label that starts with the characters '_:', which is exactly what we don't want to say. In the newer draft of the MT, I found that I needed to write things like 'bNode identifier' to refer to the items in the Ntriples syntax, ie things like _:name , since if I call them 'bNodes' it sounds like I'm saying that a node is in a document. I know that we have an investment in the 'bNode' terminology, but I wonder if it would be worth changing it, since this issue seems to (still) generate so much smoke and heat. Also, BTW, although this is looking ahead, if we allow literals as subjects and we also have literal datatyping, then we will probably need to use node identifiers even for non-blank (literal) nodes in Ntriples, since the datatyping has to be attached to the node rather than the node label. So the more neutral terminology might be even more beneficial. If we find ourselves having to talk about blank nodes labelled with literals we will be in deep confusion. >NOTE: it has been proposed that the RDF graph syntax can be used >for form a query, in which bNodes may be interpreted as query >variables. This resolution confirms that bNodes can be >distinguished from other labelled nodes within the graph syntax, but >is silent about if and how the graph syntax might be used to >represent a query. It might be better to just be silent about this entire issue (?) >This resolves specific questions in the original issue raised thus: > >[1.] Should anonymous resources have URI's? >-- No (point 1 above). As labels in the RDF graph, no. In general, is a matter on which we choose to be silent. >[2.] If so, should they be clearly distinguishable as parser generated URI's? >-- Not applicable: the parser is not required to generate URIs. If they exist and if an RDF processor can see them, then it needs to know that they are NOT intended to be part of the RDF graph. >[3.] Should there be a standard algorithm for generating URI's which ensures > that different parsers generate the same URI's from the same source > input document? >-- No: the parser is not required to generate URIs. Right. > >[4.] How might these automatically generated URI's be affected by changes > in the source document? >-- There no automatically generated URIs to be affected. >]]] Right. However, if there were any, for some external reason, then the answer to this question would have no bearing on the RDF meaning of the graph, or on any source document with the same meaning. Pat -- --------------------------------------------------------------------- IHMC (850)434 8903 home 40 South Alcaniz St. (850)202 4416 office Pensacola, FL 32501 (850)202 4440 fax phayes@ai.uwf.edu http://www.coginst.uwf.edu/~phayes
Received on Friday, 12 October 2001 15:33:24 UTC