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Re: the idea of a 'reserved' vocabulary

From: Graham Klyne <Graham.Klyne@MIMEsweeper.com>
Date: Fri, 14 Jun 2002 08:13:40 +0100
Message-Id: <5.1.0.14.2.20020614080503.0451cd80@joy.songbird.com>
To: patrick hayes <phayes@ai.uwf.edu>
Cc: w3c-rdfcore-wg@w3.org

The broad thrust looks good to me.  I have a couple of comments - one nit 
and one more substantive.

At 07:08 PM 6/13/02 -0500, patrick hayes wrote:

>Here's a rough draft of what Id like to say in the RDF MT document about 
>'reserved' (we don't say 'dark' these says) vocabulary, to give you an 
>idea of what is being proposed here.
>
>------
>What does it mean to assert an RDF graph? The normal answer is that each 
>triple can be read as a simple proposition, and the graph as a whole 
>represents the conjunction of all of these propositions, so that what is 
>asserted is the content of all the triples in the graph. Asserting a 
>triple amounts to saying that it is true, and what that means, in turn, 
>depends on what defines the meanings of the terms used in the graph. 
>Before discussing that in more detail, we first note that it is also 
>possible to use RDF triples simply as a data-structuring mechanism for 
>encoding expressions of other languages which have a more complex syntax. 
>If those 'encoding' triples are regarded as assertions in the same way as 
>other triples, complexities can arise because the meaning they would have 
>when seen simply as RDF assertions might not correspond to their intended 
>interpretation in the other language. To accommodate such encodings and 
>avoid these complications, we allow that some urirefs may be declared to 
>be 'reserved'. Triples using urirefs from any reserved vocabulary can be 
>present in an RDF graph but do not themselves make any RDF assertions. 
>They may, however, be part of an encoding of expressions in some other 
>language which itself may be asserted by the RDF graph in question, 
>according to the semantic rules of that other language. We note that an 
>RDF parser or processor is not required to treat such triples in any 
>special way,

Nit:  add "(other than that any such triples not having any affect on the 
truth or entailments of a graph)" or something like that.

>unless it also needs to access the content expressed in that other 
>language encoded in an RDF graph.
>
>Since reserving a vocabulary effects the meaning of RDF, the authority to 
>declare a uriref or urirefs 'reserved' in this sense rests with the 
>W3C.  A uriref or set of urirefs is reserved only if it is declared to be 
>so by a W3C Recommendation. In particular, reserving a vocabulary cannot 
>be done by simply asserting on a webpage that it is to be considered 
>reserved. There is no way to state in RDF, or any language encoded in RDF, 
>that a uriref is reserved, or for any RDF document to entail this as a 
>consequence.

My more substantive comment:  some folks are going to have to implement 
this stuff, and the above statement doesn't really help them.  Therefore, I 
think the spec should state up-front the form of URIs that won't be 
asserted.  To alleviate the issues of URI-inspection, I think we could 
limit the form to something like:

     http://www.w3.org/2002/06-rdf-unasserted#<foo>

where values of <foo> must be documented in W3C recommendation track 
documents.  Effectively, this designates a single URI for dark triples, for 
which there will be a single associated schema document listing the URIrefs 
whose use suspends statement-assertion.

>And then the basic MT rule for I(E) is slightly modified so that it reads:
>
>If E is a triple S P O . then I(E)=true if S, P and O are not reserved and 
>....
>
>-----
>
>That is all that is being suggested. And yes, this is the old 'unasserted 
>triples' idea in a slightly updated form.

Death to weasles!

#g


-------------------
Graham Klyne
<GK@NineByNine.org>
Received on Friday, 14 June 2002 03:37:29 EDT

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