W3C home > Mailing lists > Public > public-rdf-comments@w3.org > October 2013

Re: RDF Semantics - datatypes and "identifies" vs "denotes" - ISSUE-145

From: Pat Hayes <phayes@ihmc.us>
Date: Mon, 28 Oct 2013 23:53:20 -0500
Cc: public-rdf-comments <public-rdf-comments@w3.org>
Message-Id: <4F5E4564-58F3-456A-AB6C-2002D30EF505@ihmc.us>
To: David Booth <david@dbooth.org>

On Oct 28, 2013, at 8:55 PM, David Booth <david@dbooth.org> wrote:

> Hi Pat,
> 
> I'm trying to understand the rationale for defining the notion of "identifies" as being distinct from "denotes".  

The RDF semantics *defines* the notion of denotation. It *uses* the notion of identification, which is also used and described in a number of other W3C standards and publications. The RDF semantics document does not set out to define this notion: it simply refers to it as being any any widely accepted notion of how IRIs map to meanings which is used and accepted externally to RDF.  Thus, for example, the IRI  http://www.w3.org/2001/XMLSchema#int *identifies* the datatype called 'int' defined in section 3.4.17 of the W3C XML Schema Definition Language (XSD) 1.1 Part 2 Recommendation published on 5 April 2012, http://www.w3.org/TR/xmlschema11-2/#int. That this is true is not determined by anything in the RDF semantics: it is simply a fact, established by a complex set of social, linguistic and technical conventions about how certain IRIs are attached to accepted meanings. In order to ensure that RDF denotation agrees with this, so that interpretations  (in appropriate cases) map 'http://www.w3.org/2001/XMLSchema#int' to that datatype, it is necessary to stipulate that denotation as defined in RDF coincides with this socially defined mapping from IRIs to meanings; and that, in turn, requires that we have a way to refer to this (and similar) mappings. That is why we use the term "identify" in the RDF Semantics document to refer to this (indeed to any defined-externally-to-RDF) mapping. (We could just say something like, these IRIs denote what everyone would expect them to denote, but that would probably not be considered to be acceptably precise.)

> As I mentioned before, at first reading this appeared to me to be a contrived distinction that was created to avoid having a URI denote more than one thing. 

That was not the purpose of making the distinction.

>  But you argued that it was needed for the datatype semantics to work out, so I wanted to understand that.
> 
> http://www.w3.org/TR/2013/WD-rdf11-mt-20130723/#literals-and-datatypes
> 
> Section 7 says: "We assume that a recognized IRI identifies a unique datatype wherever it occurs, and the semantics requires that it refers to this identified datatype."  Therefore, for a recognized IRI, the "identifies" mapping is the same as the "denotes" mapping.  So at least for recognized IRIs, there appears to be no need to distinguish between "identifies" and "denotes".

The necessity is to make the assertion, that in this case denotation is (defined to be) identical to identification, not be a tautology. As it stands, this is a definition (of denotes) which uses an predefined term (of identifies) in its body. If these two terms were considered to be identical in meaning, this definition would be vacuous. But in any case, they are not identical in *meaning*.

>  Is the distinction then needed for non-recognized IRIs?  But I don't think I saw any semantic conditions or entailment rules for non-recognized IRIs.  Are there some that I missed?  I'm not seeing how the datatype semantics requires a distinction between "identifies" and "denotes".  Can you explain?  Please feel free to shift your reply to www-archive@w3.org instead of posting to this list.
> 
> Also, a few small editorial issues/typos:
> 
> 1. Two typos in this sentence: "RDF processors which are not able to determine which datatype is identifier by an IRI cannot recognize that IRI, and should treat any literals type with that IRI as unknown names."
> s/identifier/identified/
> s/type/typed/

Yes, others had noted these. Now fixed.

> 
> 2. "Such literals SHOULD be treated like IRIs and assumed to denote" should be "Such literals SHOULD be treated like IRIs and SHOULD be assumed to denote"?

No, because this follows from the first. But it could read " ...SHOULD be treated like IRIs and hence assumed to denote..."

> 
> 3. "A literal with datatype d denotes the value obtained by applying this mapping to the character string sss: L2V(d)(sss)." should be "A literal composed of character string sss with datatype d denotes the value obtained by applying this mapping to sss: L2V(d)(sss)."?

Yes, I will make that change in the next edit. 

Pat

> 
> Thanks,
> David
> 

------------------------------------------------------------
IHMC                                     (850)434 8903 home
40 South Alcaniz St.            (850)202 4416   office
Pensacola                            (850)202 4440   fax
FL 32502                              (850)291 0667   mobile (preferred)
phayes@ihmc.us       http://www.ihmc.us/users/phayes
Received on Tuesday, 29 October 2013 04:53:46 UTC

This archive was generated by hypermail 2.3.1 : Tuesday, 6 January 2015 20:29:58 UTC