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Re: refining closure text for rdfs-isDefinedBy-semantics

From: Dan Brickley <danbri@w3.org>
Date: Fri, 7 Jun 2002 09:56:13 -0400 (EDT)
To: <w3c-rdfcore-wg@w3.org>
Message-ID: <Pine.LNX.4.30.0206070922260.28380-100000@tux.w3.org>


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.
Received on Friday, 7 June 2002 09:56:14 EDT

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