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Equality versus Convertability

From: Patrick Stickler <patrick.stickler@nokia.com>
Date: Mon, 11 Aug 2003 10:14:24 +0300
Message-ID: <006501c35fd8$35177410$de0ca20a@NOE.Nokia.com>
To: <w3c-rdfcore-wg@w3.org>

I like the idea proposed by Frank during the last conference 
call that insofar as the MT is concerned, the value space of
rdfs:XMLLiteral is disjunct from all XSD value spaces, and 
from the set of plain literals, *BUT* that we somewhere note 
that one may apply regular (1:1), bidirectional "conversions"
(or "coercions") between the members of the value spaces
of particular pairs of datatypes.

Thus, while "1"^^xsd:integer and "1.0"^^xsd:float are
semantically distinct values and are not equal, one
may convert between them (coerce the value from one
datatype to the other), back and forth, as often as
one likes, without any loss of meaning.

Likewise, while "foo"^^rdfs:XMLLiteral and "foo" (a plain
literal without lang tag) and "foo"^^xsd:string are all
semantically distinct values, one may convert between them
freely. In fact, we can expect RDF applications to do this
frequently.

I think this distinction between equality versus regular
bidirectional convertability addresses the two previously
(thought to be conflicting) needs of keeping the MT sane
(by keeping value spaces disjunct) and yet capturing the 
common intuition that certain datatypes still have a kind
of 1:1 intersection of values. That intersection is thus not
equality, but 1:1 bidirectional convertability.

I think we can use this idea of convertability to finesse
solutions to the remaining issues regarding the relationships
between XML literals, plain literals, xsd:string, and in
the future, between XML literals and XSD complex types.

Knowing that such 1:1 conversion relations can be defined to 
hold between datatypes alleviates my concerns about defining
value spaces as disjunct.

Patrick
Received on Monday, 11 August 2003 03:14:35 EDT

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