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RE: RDF datatyping goals (action from teleconference)

From: Graham Klyne <Graham.Klyne@MIMEsweeper.com>
Date: Sun, 13 Jan 2002 12:29:23 +0000
Message-Id: <5.1.0.14.2.20020113114610.00a878f0@joy.songbird.com>
To: "Jeremy Carroll" <jjc@hplb.hpl.hp.com>
Cc: "RDF core WG" <w3c-rdfcore-wg@w3.org>
At 08:38 PM 1/11/02 +0000, Jeremy Carroll wrote:

>Typo?
>
>I think you missed the following from Idiom B example:
>
>exB:birthDate rdfs:range exP:date.lit .

Not so much a typo (that was what I intended to write), but I agree there's 
something here that needs to be handled more carefully.

I was trying to distinguish idioms in which schema statements are given 
explicitly in a graph, and idioms for which they are implied.  I think that 
was sloppy on my part, and needs more careful handling.

I think there are three kinds of schema-related usage pattern that we may 
wish to consider:
(a) schema statements included explicitly in the same RDF document
(b) schema statements referenced in a separate RDF document
(c) schema statements implied and "understood" by the processing application

[Case (c) is messy, in that it doesn't really form a basis for the proposed 
vision of information exchange via RDF.  But that is the way that I think 
some single-application RDF specifications are being developed.  It's how 
current CC/PP implementations work.]

I'll argue that a non-schema-aware application that operates per (c) is 
semantically equivalent to schema-aware application that operates per 
(b);  a (b) application can exchange information with a (c) application 
(presuming the appropriate schema document can be discovered for (b)).

I'll also argue that (a) is semantically equivalent to (b) in the sense 
that if an RDF graph and any associated schema graphs are merged, the 
result can be interpreted per (a).

So, we have three usage patterns that are equivalent, modulo the physical 
location or otherwise of the schema statements (which I might call (a) 
internal, (b) external and (c) implied).

This suggests to me that the idioms in the datatyping desiderata would 
better be presented in two parts:  "direct statements" from which some 
meaning is directly derived, and schema statements that help to define the 
environment for evaluation of the direct statements.

Then we would get the following -- I'll write direct statements above the 
line, and schema statements below the line.  The denotation of the ex*:Date 
identifiers is presumed to be understood by applications that exchange 
information, this being their common understanding/implementation of some 
datatyping scheme.


Idiom A:

   person:Jenny exA:birthDate
     [ exA:date "2001-07-15" ] .
   -------------------------------------------------


Idiom B:

   person:Jenny exB:birthDate "2001-07-15" .
   -------------------------------------------------
   exB:birthDate rdfs:range exB:date .


Idiom P:

   person:Jenny exP:birthDate "2001-07-15" .
   -------------------------------------------------
   exP:birthDate rdfs:range exP:date .


Idiom D:

   Jenny exD:birthDate
     [ rdf:value "2001-07-15" ;
       rdf:type exD:date ] .
   -------------------------------------------------


Although they are so-far identical, I've left idioms B and P separate in 
case we find some more detailed usages based in the underlying assumptions 
that show up differently.

If you think this adequately addresses the point you raised, I'll update 
the desiderata document to reflect these changes.

#g



------------------------------------------------------------
Graham Klyne                    MIMEsweeper Group
Strategic Research              <http://www.mimesweeper.com>
<Graham.Klyne@MIMEsweeper.com>
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Received on Sunday, 13 January 2002 07:34:27 EST

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