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Re: names for resources

From: Dan Connolly <connolly@w3.org>
Date: Fri, 11 Nov 2005 09:40:32 -0600
To: Eric Prud'hommeaux <eric@w3.org>
Cc: public-rdf-dawg@w3.org
Message-Id: <1131723632.12579.161.camel@dirk>

On Fri, 2005-11-11 at 09:52 -0500, Eric Prud'hommeaux wrote:
> I took a while to get back to this as I was on vacation. Apologies.
> 
> On Sun, Oct 30, 2005 at 08:18:44AM -0600, Dan Connolly wrote:
> > 
> > On Sun, 2005-10-30 at 04:59 -0500, Eric Prud'hommeaux wrote:
> > > SPARQL differentiates between IRIs, Literals and Blank Nodes. A term
> > > for IRI shows up in the definition of the isIRI test. STR, as well the
> > > return type of DATATYPE. Originally, I used terms like "RDF URI" and
> > > "RDF literal" to define the semantics and return types of functions.
> > > At some point, I thought it would be a good idea to switch to
> > > rdfs:Resource and rdfs:Literal. But rdf:Resource is EVERYTHING, so I
> > > needed another term.
> > > 
> > > DanC suggested xsd:anyURI. This promotes all strings of type
> > > xsd:anyURI to RDF resource.
> > 
> > Everything is an RDF resource. So there's no "promotion".
> 
> AGG! We need 2 different terms here. There are things that the RDF
> Model calls URIrefs, and there are resources:
> 
>          Resources
>        /    |     \
> URIrefs  literals  bNodes

Yes, that's an accurate picture, where the lines
represent rdfs:subClassOf.

Note that the term "URIref"
is obsolete in favor of IRI. SPARQL is defined in terms
of IRIs.

> We specifically need a name for URIrefs because it:
>   1. is the return type of DATATYPE()

yes, xsdt:anyURI works well there.

>   2. defines the semantics of isIRI()

well, isIRI is a function of *terms*, not what
the terms denote. It doesn't really depend on what URI we
use for the class of URIrefs/IRIS.

>   3. defines the semantics of STR()

I don't see any connection to STR().


> > >  For instance, if I write some XML:
> > >   <foo bar="4" baz="http://www.w3.org/"/>
> > > , validate it by some W3C XML Schema:
> > >   <xs:element name="foo">
> > >     <xs:complexType>
> > >       <xs:attribute name="bar" type="xs:integer"/>
> > >       <xs:attribute name="baz" type="xs:anyURI"/>
> > > and write out the PSVI as RDF, I am making an assertion about the
> > > resource <http://www.w3.org/> (didn't look up the *real* PSVI
> > > projection in to RDF here):
> > >   [ a Element; 
> > >     hasAttribute [ 
> > >       name "bar", 
> > >       value 4 ] ,
> > >     hasAttribute [ 
> > >       name "baz", 
> > >       value <http://www.w3.org/> ] ]
> > 
> > no, it would be: value "http://www.w3.org/"
> 
> I can imagine justifications for either <http://www.w3.org/> or
> "http://www.w3.org/"^^xsd:anyURI , but "http://www.w3.org/" makes
> no sense at all to me. Why does the thing with the lexical form "4"
> and the type xs:integer turn into an integer, but the thing with
> the lexical form "http://www.w3.org/" and the type xsd:anyURI not
> turn into at least one of those?

OK, "http://www.w3.org/"^^xsd:anyURI .

I didn't catch the subtlety of the value property; I thought
it gave the/a lexical representation. I read too quickly.


> > > However, this approach require a couple exceptions that I'm not
> > > comfortable with:
> > > 
> > > In general, datatypes can be transformed with
> > > STR:
> > >   STR("asdf"^^foo:bar) = "asdf"
> > > DATATYPE:
> > >   DATATYPE("asdf"^^foo:bar) = foo:bar
> > > and ^^ casting:
> > >   "asdf"^^xsd:integer = "asdf"^^xsd:integer
> > > 
> > > This (I believe, though this merits a test case) holds for SPARLE terms:
> > >   STR(4) = "4"
> > >   DATATYPE(4) = xsd:integer
> > >   "4"^^xsd:integer = 4
> > > 
> > > Some of these functions still work for URIs:
> > >   STR(<http://www.w3.org/>) = "http://www.w3.org/"
> > > and maybe DATA
> > >   DATATYPE(<http://www.w3.org/>) = xsd:anyURI
> > 
> > no; the datatype of W3C's homepage isn't xsd:anyURI. Use/mention bug.
> > 
> > The xsd:anyURI datatype works just like all the others:
> 
> "just like"?
> I don't think you're arguing constructively here. We need to figure
> out exactly what you think xsd:anyURI is.

I think it's what the W3C XML Schema recommendation says it is.

>  Either you are conflating
> two nodes that are distinct in RDF semantics:
>   the URIref <http://www.w3.org/>
>   the typed literal "http://www.w3.org/"^^xsd:anyURI
> or you are saying that
>   the typed literal "http://www.w3.org/"^^xsd:anyURI
> doesn't exist, or you are saying that SPARQL does not allow you to
> distinguish the difference.
>   DATATYPE(<http://www.w3.org/>) = DATATYPE("http://www.w3.org/")

Indeed, SPARQL doesn't assign any meaning to
  DATATYPE(<http://www.w3.org/>)

and hence doesn't really allow you to distinguish the difference
between DATATYPE(<http://www.w3.org/>) and anything else.


> > DATATYPE("http://www.w3.org/"^^xsd:anyURI) = xsd:anyURI
> > and
> > str("http://www.w3.org/"^^xsd:anyURI) = "http://www.w3.org/"
> 
> > > but we don't really "know" the lexical form for URIs
> > 
> > We know the lexical form for URI literals. URI literals
> > are self-denoting;t hey work differently from <xyz> symbols.
> > 
> > >  so
> > >   "http://www.w3.org/"^^xsd:anyURI != <http://www.w3.org/>
> > > 
> > > 
> > > I don't think it's a good idea to invent a term or syntax for this, so
> > > I'm in favor of going back to a term that's not a URI (RDF Resource).
> > 
> > Which do you mean? URI or Resource? Remember, _everything_ is a
> > resource.
> 
> URIref

xsd:anyURI is the W3C Recommended URI for the class/datatype of IRIs.
(well, the class is actually a bit larger; it includes relative URI/IRI
references too. But it's close enough for our purposes.)

> > > There is a precedent for this in SPARQL ("RDF term", "blank node") and
> > > in XPath Functions and Operators ("numeric").
> > > 
> > > 
> > > I'm on vacation this week in Italy. I'd like to resolve this when I
> > > get back.
> > 
> > What is it that you'd like to resolve?
> > 
> > > 
> > > 
> > > Earlier thread:
> > >   http://www.w3.org/mid/20050911103218.GF17622@w3.org
> 
-- 
Dan Connolly, W3C http://www.w3.org/People/Connolly/
D3C2 887B 0F92 6005 C541  0875 0F91 96DE 6E52 C29E
Received on Friday, 11 November 2005 15:40:38 GMT

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