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Re: refining closure text for rdfs-isDefinedBy-semantics

From: Graham Klyne <Graham.Klyne@MIMEsweeper.com>
Date: Fri, 07 Jun 2002 18:03:42 +0100
Message-Id: <5.1.0.14.2.20020607175112.03c7ddd0@joy.songbird.com>
To: Dan Brickley <danbri@w3.org>
Cc: <w3c-rdfcore-wg@w3.org>

Dan,

I'm a little uneasy about aspects of this, but I'm also not sure if it 
really matters, so I'll try to be brief.

I'm uneasy about this idea of "the" context in which a property is 
defined.  Isn't this something of a departure from the idea that, in RDF, 
anyone can say anything about anything?  Also, is it really appropriate 
that there is a *single* schema for any property?   The kinds of statements 
that appear in RDF schema could legitimately appear in any RDF 
document;  what is the distinguishing feature of "the" schema here?

OTOH, some thoughts about the role of fragment identifiers expressed by 
TimBL, and recently in different words by me [1], suggest that there is 
sometimes a role for a "distinguished" RDF document (possibly notional) in 
relation to some RDF resources.

But overall, I'm thinking that if there is to be just _one_ correct 
rdfs:isDefinedBy property for a resource, I think some justification for 
its distinguished status is called for.

#g
--

[1] http://lists.w3.org/Archives/Public/www-talk/2002MayJun/0032.html


At 09:56 AM 6/7/02 -0400, Dan Brickley wrote:


>On Fri, 24 May 2002, Dan Brickley wrote:
>
> > I raised some minor concerns with this.
> > http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2002May/0030.html
>...and subsequent telecon discussion and some huge mailing list threads on
>www-rdf-interest and dc-architecture suggest there is further need for
>clarification.
>
>I fear this could drag on, and propose we stick with a solution based
>on the design from Model and Syntax REC and the RDF Schema CR.
>
>This would go as follows:
>
>First, background context and constraints on our options:
>
>         http://www.w3.org/TR/REC-rdf-syntax/#usage
>         C.2. Namespace URIs
>
>         [[
>         RDF uses the proposed XML namespace mechanism to implement globally
>         unique identifiers for all properties. In addition, the namespace 
> name
>         serves as the identifier for the corresponding RDF schema.  The
>         namespace name is resolved to absolute form as specified by the
>         algorithm in Section 5.2., Resolving Relative References to Absolute
>         Form, in [URI].  An RDF processor
>
>         can expect to use the schema URI to access the schema content. This
>         specification places no further requirements on the content that 
> might be supplied at
>         that URI, nor how (if at all) the URI might be modified to obtain
>         alternate forms or a fragment of the schema.
>         ]]
>
>
>         http://www.w3.org/TR/REC-rdf-syntax/#basic
>         [[
>         2.2.3. Schemas and Namespaces
>         ...
>
>         In RDF, each predicate used in a statement must be
>         identified with exactly one namespace, or schema.
>
>         ]]
>
>And reminding ourselves of the longer explaination of rdfs:isDefinedBy in
>the old Candidate Recommendation for RDF Schema, ie.
>
>         http://www.w3.org/TR/2000/CR-rdf-schema-20000327/#s2.3.5
>
>         [[
>         The property rdfs:isDefinedBy is a subproperty of
>         rdfs:seeAlso, and indicates the resource
>         defining the subject resource. As with rdf:seeAlso, this
>         property can be applied to any instance of rdfs:Resource and may have
>         as its value any rdfs:Resource.
>         The most common anticipated usage is to identify an RDF schema, 
> given a
>         name for one of the properties or classes defined by that schema.
>         Although XML namespace declarations will typically provide the 
> URI where
>         RDF
>         vocabulary resources are defined, there are cases where additional
>         information is required.
>         For example, constructs such as
>         <rdfs:subPropertyOf
>         rdf:resource="http://purl.org/dc/elements/1.0/Creator"/>
>         do not
>         indicate the URI of the schema that includes the vocabulary item
>         Creator (i.e., http://purl.org/dc/elements/1.0/).
>         In such cases, the rdfs:isDefinedBy property can be used to 
> explicitly
>         represent that
>         information. This approach will also work when the URIs of the 
> namespace
>         and its components have no obvious relationship, as would be the 
> case if
>         they
>         were identified using schemes such as GUIDs or MD-5 hashes.
>         ]]
>
>
>
>We can note that:
>
>RDF provides a property rdfs:isDefinedBy that is a specialisation of the
>rdfs:seeAlso property. This property is used to relate an RDF vocabulary
>term (such a Class or Property) to the context within which it
>is defined.
>
>For every RDF property there is exactly one correct value for the
>rdfs:isDefinedBy property.
>
>When RDF graphs are written in the RDF/XML 1.0 syntax, this value
>corresponds to the XML namespace URIref used in the serialized
>representation of the RDF properties.
>
>....
>
>can we take this as a basis for progress?
>
>The main clarification is that we represent explicitly the M+S claim that
>there is just one schema for each property, and that rdfs:isDefinedBy
>can thus be used to represent (within the RDF graph) the relationship that
>holds between a property and the namespace within which it is defined.
>
>Dan
>
>
> >       - isDefinedBy is a Property
> >       - it has no further semantics in the RDF Model Theory
> >
> >       - further sub-properties of it may be created by others
> >       - RDF Core doesn't currently expect to create any of these.

-------------------
Graham Klyne
<GK@NineByNine.org>
Received on Friday, 7 June 2002 13:29:48 EDT

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