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Re: RDF Graph questions

From: patrick hayes <phayes@ai.uwf.edu>
Date: Tue, 28 May 2002 18:00:16 -0500
Message-Id: <p0511170db91990389edf@[65.217.30.61]>
To: "Jeremy Carroll" <jjc@hplb.hpl.hp.com>
Cc: w3c-rdfcore-wg@w3.org
>First, a heads up on my action to write a section defining the RDF
>graph.
>It's progressing, attached (with the usual red and green), still
>unfinished, and what is done is quite rough (no consistency in term use,
>or capitalization etc. I still need to do my own checking on readability
>etc.).

Quick comment: its dangerous to simply say that the RDF graph *is* a 
graph, even in brief, as in 2 para 1. I got hauled over the 
mathematical coals for saying this, since technically its not a graph 
as in graph theory, not even a labelled one (graphs can't have more 
than one arc between 2 nodes, and labelled graphs are graphs with 
labels added.)

>
>Second a few questions.
>
>1. Are there unattached nodes in an RDF graph?

  If we define an RDF graph to be a set of triples, then the answer is 
no automatically.

>
>2. Can any URI ref be a property name or must there be some associated
>namespace?

Any, no associated namespace (What does 'associated' mean??)

>3. For XML literals should I
>    - specify that they must be well-balanced XML
>    - explicitly permit any unicode string (but only constrain equality
>for well-balanced XML)
>    - have deliberate vagueness (e.g. talk about a unicode string, and
>then only define equality on well-balanced XML and ignore the issue of
>whether other strings are permitted or not).

I have no opinion on this one.

>
>Test cases for 1 & 2.
>
>1:
>
>Is this RDF/XML document
>
><rdf:RDF><rdf:Description/></rdf:RDF>
>
>equivalent to or different from this one:
>
><rdf:RDF/>
>
>
>and/or this one:
>
><rdf:RDF>
>  <rdf:Description rdf:about="http://example.org/"/>
></rdf:RDF>
>
>
>(the question can't be asked in N-triple)

Which ought to give you a hint :-)

>
>2:
>
>http://www.w3.org/2000/10/rdf-tests/rdfcore/rdfms-uri-substructure/error
>001.nt
>
>whose status is pending
>
>Is this:
>
>a) an error because there is no such RDF graph
>
>or
>
>b) an example of alegal RDF graph that cannot be serialized as RDF/XML

Id say the latter. The graph certainly can be drawn, described in 
Ntriples, and has a model-theoretic meaning. Also it can be inferred 
from a graph that can be XML serialized.


Pat
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Received on Tuesday, 28 May 2002 18:59:35 EDT

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