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One last proposal before we close...

From: Patrick Stickler <patrick.stickler@nokia.com>
Date: Fri, 11 Jul 2003 19:51:41 +0300
Message-ID: <000901c347cc$b87f5940$a80da20a@NOE.Nokia.com>
To: "rdf core" <w3c-rdfcore-wg@w3.org>
Cc: "duerst" <duerst@w3.org>, "w3c-i18n-ig" <w3c-i18n-ig@w3.org>


The following is a refinement to the original proposal
(alternative 1) which clarifies the distinction between
contextual literals and non-contextual literals (i.e.
traditional M&S literals and datatyped literals) which
I think would be reasonable still for the WG to consider.

Please see the end for the motivations for still making
such a proposal after todays telecon.

--

Changes:

1. The datatype rdf:XMLLiteral is discarded, or at
least moved to an appendix as optional/useful.

2. The attribute+value rdf:parseType="Literal" is
strictly syntactic, indicating a plain literal
which is serialized in the RDF/XML instance as XML.
I.e. a literal constituting text with markup.

3. The attribute rdf:datatype can co-occur with
rdf:parseType="Literal".

4. If no rdf:datatype is specified along with
rdf:parseType="Literal", this creates a contextual
literal, such that any xml:lang, xml:base, namespaces,
etc. in scope for the literal contribute to its
interpretation, and via canonicalization and lang
tag, are reflected in the graph.

5. The presence of rdf:datatype, with or without
rdf:parseType="Literal" creates a non-contextual
typed literal, where any xml:lang, xml:base,
namespaces, etc. in scope for the literal are
irrelevant to its interpretation and not reflected
in the graph.

--

Thus, given a context of

   <rdf:RDF ... xml:lang="fi" xmlns:xhtml="...">
      ...
   </rdf:RDF>

all of the following:

1. <rdf:Description rdf:about="#x">
      <ex:foo>bar</ex:foo>
   </rdf:Description>

2. <rdf:Description rdf:about="#x">
      <ex:foo rdf:parseType="Literal">bar</ex:foo>
   </rdf:Description>

3. <rdf:Description rdf:about="#x" ex:foo="bar"/>

generate the same triple:

  <#x> ex:foo "bar"@fi .

--

All of the following:

4. <rdf:Description rdf:about="#x">
      <ex:foo rdf:parseType="Literal"><xhtml:b>bar</xhtml:b></ex:foo>
   </rdf:Description>

5. <rdf:Description rdf:about="#x">
      <ex:foo>&lt;xhtml:b&gt;bar&lt;/xhtml:b&gt;</ex:foo>
   </rdf:Description>

6. <rdf:Description rdf:about="#x"
ex:foo="&lt;xhtml:b&gt;bar&lt;/xhtml:b&gt;"/>

generate the same triple:

   <#x> ex:foo "<xhtml:b xmlns:xhtml="...">bar</xhtml:b>"@fi .

--

Both of the following:

7. <rdf:Description rdf:about="#x">
      <ex:foo rdf:datatype="&ex;blargh">bar</ex:foo>
   </rdf:Description>

8. <rdf:Description rdf:about="#x">
      <ex:foo rdf:datatype="&ex;blargh" rdf:parseType="Literal">bar</ex:foo>
   </rdf:Description>

generate the same triple:

   <#x> ex:foo "bar"^^ex:blargh .

--

And both of the following:

9. <rdf:Description rdf:about="#x">
      <ex:foo rdf:datatype="&ex;blargh"
rdf:parseType="Literal"><xhtml:b>bar</xhtml:b></ex:foo>
   </rdf:Description>

10.<rdf:Description rdf:about="#x">
      <ex:foo
rdf:datatype="&ex;blargh">&lt;xhtml:b&gt;bar&lt;/xhtml:b&gt;</ex:foo>
   </rdf:Description>

generate the same triple:

   <#x> ex:foo "<xhtml:b>bar</xhtml:b>"^^ex:blargh .

** Note: if a non-contextual XML fragment does not itself specify
         all relevant namespace declarations locally, they are not
         taken from the surrounding RDF/XML context. They may, by
         design, be provided by the context into which the fragment
         is inserted. The XML fragment is a 'true' fragment, not
         a fragment extracted out of the context of an XML instance.

--

The changes to the specs required for this are (IMO)
quite minimal.

1. The RDF/XML syntax must be modified to allow co-occurrance
of rdf:datatype and rdf:parseType="Literal".

2. The mapping from RDF/XML must be finessed slightly, but
there are no new operations involved, only a change in when
they are applied.

No changes are required to the graph syntax, N-Triples, or
the MT (though Pat needs to confirm the latter, the MT may in
fact require a few minor tweaks to the wording).

--

Such a solution draws a clear distinction between the use
of XML for textual markup versus the use of XML for data
markup, and allows different users to choose the optimal
type of literal, contextual or non-contextual, as they see
fit.

It is clear in the abstract graph which is which.

Equivalences between contextual and non-contextual literals
can be addressed separately from the RDF specs, as appropriate.

--

The motivation for promoting this slight change is the
realization that in the long and arduous processs of
getting to where we are now with datatyping, it was
overlooked that use of RDF datatyping with complex
types would be greatly facilitated by the ability to
serialize complex typed literals as XML in RDF/XML.

It is true that the present solution does not prohibit
the use of complex types. But it does, though, require
any complex type other than rdf:XMLLiteral to be fully
escaped in the RDF/XML.

This new approach allows the expression of statements
such as:

<rdf:Description rdf:about="#x">
   <ex:contact rdf:parseType="Literal" rdf:datatype="&vcard;N">
      <vCard:N xmlns:vCard="http://www.w3.org/2001/vcard-rdf/3.0#">
        <vCard:Family> Crystal </vCard:Family>
        <vCard:Given>  Corky </vCard:Given>
      </vCard:N>
   </ex:contact>
</rdf:Description>

<rdf:Description rdf:about="&ex;contact">
   <rdfs:range rdf:resource="&vCard;N"/>
</rdf:Description>

etc...

Anyway, I think the WG should at least consider it. In the
interests of both the I18N concerns as well as tighter
synergy between RDF and XML Schema.

--

At the very least, we might consider the allowance of
an explicit rdf:datatype specification for XML literals,
leaving rdf:XMLLiteral as a default if unspecified,
even if nothing else is changed.

Regards,

Patrick
Received on Friday, 11 July 2003 12:51:56 EDT

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