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rdf:about and owl:sameIndividualAs oddities

From: Jimmy Cerra <jimbobbs@hotmail.com>
Date: Thu, 1 May 2003 22:12:21 -0400 (EDT)
To: public-webont-comments@w3.org
Message-ID: <000001c31050$3becd230$0100a8c0@drsoong>




Hey,

I've been reviewing OWL, and a strange idea occurred to me.  In rdf,
"blank nodes" are distinct resources.  However, the "thing" that they
are describing is undefined [1].  The following is an example:
 
<rdf:Description>
	<dc:creator>Roy G. Biv</dc:creator>
</rdf:Description>

However, using OWL, I could identify the resource by identifying a
resource which is the same as the blank one:

<rdf:Description>
	<owl:sameIndividualAs rdf:resource="#foobar" />
	<dc:creator>Roy G. Biv</dc:creator>
</rdf:Description>

However, the meaning of the above statements is equivalent to a
"non-blank" node describing "#foobar", as in:

<rdf:Description rdf:about="#foobar">
	<dc:creator>Roy G. Biv</dc:creator>
</rdf:Description>

One could theoretically define the identity of all objects in that
manner.  However, that would be confusing.  Should identifying blank
resources with OWL, instead of RDF, be depreciated?

I think that having two mechanisms for identifying a resource is "messy"
and makes the grammar combination of RDF+OWL inconsistent.  Except for
different ranges, owl:sameIndividualAs (range=resource) and rdf:about
(range=string) mean the same thing.  The extra syntax seems redundant.

If rdf:about was an actual property, then the two concepts could be
combined.  Furthermore, if the property-as-attribute abbreviation for
rdf:type was applied to rdf:about as well, then the abbreviated syntax
would be identical to the 1999 xml-serialization syntax [2].  However,
this would still allow the equivalent owl:sameIndividualAs
representations, such as the below example:

<rdf:Description rdf:about="http://www.w3.org/TR/html4/strict.dtd">
<rdf:about rdf:resource="urn:publicid:-:W3C:DTD+HTML+4.01:EN" />
</rdf:Description>

The above seems much more intuitive than the OWL version:

<rdf:Description rdf:about="http://www.w3.org/TR/html4/strict.dtd">
<owl:sameIndividualAs rdf:resource="urn:publicid:-:W3C:DTD+HTML+4.01:EN"
/>
</rdf:Description>

Or even:

<rdf:Description>
<owl:sameIndividualAs
rdf:resource="http://www.w3.org/TR/html4/strict.dtd"/>
<owl:sameIndividualAs
rdf:resource="urn:publicid:-:W3C:DTD+HTML+4.01:EN"/>
</rdf:Description>

Just an idea [3].

--
James F. Cerra 

[1] http://www.w3.org/TR/rdf-concepts/#section-blank-nodes Note that the
spec says "...this set is arbitrary.  RDF makes no reference to any
internal structure of blank nodes."  I interpret this to mean that the
resource being described by a blank note is unidentified.  Since the
subject is unknown, then it must be undefined, I think.

[2]
http://www.w3.org/TR/rdf-syntax-grammar/#section-Syntax-property-attribu
tes Note "This abbreviation can also be used when the property element
is rdf:type and it has an rdf:resource attribute the value of which is
interpreted as a RDF URI Reference object node."

[3] One objection to the proposed suggestion is that it confuses the
concrete syntax for RDF/XML and the abstract syntax.  See:
http://lists.w3.org/Archives/Public/www-rdf-interest/2003Apr/0069.html
Note "I'd say this is a terrible idea"
Received on Thursday, 1 May 2003 23:38:37 GMT

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