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Re: datatype maps in Semantics and Concepts

From: Pat Hayes <phayes@ihmc.us>
Date: Tue, 26 Feb 2013 20:34:40 -0600
Cc: RDF WG <public-rdf-wg@w3.org>, Richard Cyganiak <richard@cyganiak.de>
Message-Id: <550B9CEF-47AC-4D35-BC0E-EBD92DE6B228@ihmc.us>
To: "Peter F. Patel-Schneider" <pfpschneider@gmail.com>

On Feb 26, 2013, at 7:48 PM, Peter F. Patel-Schneider wrote:

> If we want to have the standard datatypes fixed to their usual meaning, then why not just say that?

I think that "the datatype conventionally identified by" an IRI does say that. I'm open to a change of phrasing if you prefer something different. Suggestions? 

> The current document talks about "the datatype conventionally identified by aaa".  What does this end up meaning?  How are new datatypes set up?  How does "recognition" interact with "conventional indentification"? This just seems like magic to me.

Its how the Web works. People define datatypes and assign them a URI, and then other people use that URI to refer to the datatype. How did http://www.w3.org/1999/02/22-rdf-syntax-ns#PlainLiteral get to refer to the datatype we all know and love, the Edsel of the datatype world? It does so because http://www.w3.org/TR/rdf-plain-literal/ says it does. It does *not* do so because the pair 

<"http://www.w3.org/1999/02/22-rdf-syntax-ns#PlainLiteral", [the datatype described in http://www.w3.org/TR/rdf-plain-literal/] >

is in some datatype map. 

In any case, how is a new datatype set up in the current D-semantics? This is just as mysterious and magical. At least the new way of stating admits that it is just using the normal conventions of the Web to determine what datatype IRIs denote, instead of confusing things with some impressive-looking but essentially meaningless pseudo-mathematics. 

BTW, for more on this, see this exchange between Richard and Antoine (which I only just discovered):

(from  http://answers.semanticweb.com/questions/9781/regarding-plain-literal-and-rdfplainliteral-equality )


The semantics of "foo" and "foo"^^xs:string is the same only if you assume a datatype map which maps xsd:string to the corresponding XML Schema datatype. In any other situation, nothing mandates these two things to be the same (i.e., to have the same interpretation). In particular, the RDF and RDFS semantics do not mandate that (though it's likely to change in RDF 1.1, yes).
(23 May '11, 08:37)Antoine Zimm... ♦

You pedant! That's true of course, but I submit that talking about the value of a typed literal obviously assumes that the datatype is in the datatype map, and mapping xsd:string to anything but XSD's string type would be nuts.
(23 May '11, 09:05)cygri ♦  

You're right, it would be nuts! Yet it is allowed in RDF 2004, hopefully not in RDF 2013.
(23 May '11, 12:02)Antoine Zimm... ♦



> peter
> PS:  I was expecting the artist formerly known as the artist formerly known as Prince to make an appearance a bit later on.
> On 02/26/2013 05:30 PM, Pat Hayes wrote:
>> On Feb 26, 2013, at 2:11 PM, Peter Patel-Schneider wrote:
>>> The new semantics document doesn't really use datatype maps (but still has vestiges).
>>> The new treatment is new, different from Concepts, and, I think, more confusing than the old treatment.
>> Why is it more confusing? It simply singles out a set of IRIs which are assumed to denote datatypes. This is how datatypes are identified already, in fact. We all talk about (for example) xsd:string, and we know what is being referred to. We don't see any need to say, "the datatype d which such that <'xsd:string', d> is in the datatype map". The old treatment allowed for D-interpretations where (for example) the xsd datatype IRIs were interpreted to mean non-xsd datatypes in D. I don't think we need this much generality, and can rely on external specifications to define what datatype is denoted by a datatype IRI.
>> I have been trying to simplify the semantics document to eliminate needless formality and 'mathematical' style, and this is part of that simplification. The new treatment is much simpler and IMO superior. The datatype map is simply part of the interpretation mapping, which is what it always was in any case.
>>> I suggest going back to the old treatment (with modifications).
>> I suggest modifying Concepts to conform to the new treatment. It will be simpler and easier to understand. (If it would be helpful, I could draft the relevant section.)
>> Pat
>>> peter
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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 Wednesday, 27 February 2013 02:35:12 UTC

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