Dissenting Opinion: xml:lang and rdf:parseType="Literal"

@@ draft jjc - for consideration by em, bwm, danbri and WG @@

The Internationalization Working Group has registered a dissenting opinion on the treatment agreed by RDFCore concerning rdf:parseType="Literal". @@ add link to dissent, when it comes @@ This dissent is to changes made by the RDF Core working group in response to comments concerning the last call design, particularly comments concerning the datatype rdf:XMLLiteral. These changes are reflected in the September 5th publication, particularly of RDF Concepts, RDF/XML Syntax, and RDF Semantics.

This feature of RDF is the single feature to have attracted most comments both during and before last call. These included comments from Reagle ( on use of canonicalization and use of an XML wrapper), Prud'hommeaux, the Web Ontology WG, Patel-Schneider, (concerning: language tag in canonical XML; malformed literals of type rdf:XMLLiteral; typed literals and language tags; aliases of rdf:XMLLiteral; language tags in rdf:XMLLiteral in the LBase appendix), Berners-Lee , Marchiori.

Resolving these comments to the WG's (and the commentators') satisfaction involved changes that impacted aspects that were known to be important to the internationalization working group, and they were informed. Dürst then commented further (regarding language tagging and rdf:XMLLiteral, XMLLiteral and octets, using rdf:datatype="&rdf;XMLLiteral"). A detailed analysis was provided by Ishida.

The Working Group gave further consideration to the comments of Dürst and Ishida. Changes were made to avoid the problems with octets, and these were agreed by Dürst. The other arguments were not found to be compelling, for example Carroll's response to Ishida. Most of the substantive arguments had already been made in the WG decision of 9th May.

Before that decision, the WG has considered four different designs, for the result of an rdf:parseType="Literal":

A special sort of (untyped) literal

Such as in the 29th August 2002 Working Draft.

A special sort of typed literal.

Similar to the last call design. This would remain the only datatype that can have a language identifier.

A normal typed literal, with an XML wrapper

The wrapper carries an xml:lang attribute.

A normal typed literal, without an XML wrapper

This follows Exclusive XML Canonicalization, and loses the xml:lang attribute. This is the chosen design, in the current editors drafts.

In addition, further designs have been discussed as a result of the I18N comment. These include:

All literals being XML

The essence of this proposal is that plain and XML literals are the same and must both be in exclusive C14N XML. A plain literal is converted by the parser into C14N XML by escaping the special characters (such as "<") as entities.

xml:lang makes triples, with property rdf:langTag

This was dropped because it was impossible to have "chat" in French and "chat" in English in the same graph.

xml:lang's makes triples with interpretation properties

Since this was dropped since it does not address the I18N issue.

Prior to the WG decision of 9th May, participants in the WG have argued that:

• The simplicity of the current design will encourage deployment of XMLLiteral, which will aid internationalization concerns.
• The treatment of xml:lang is performed by Exclusive XML Canonicalization (which had been reviewed and accepted by the I18N WG). Note, Exclusive XML Canonicalization does not exclude the possibility of the information that is lost in the process being carried by some other mechanism.
• An RDF specific solution to perceived deficiences in exclusive canonicalization would not be interoperable with other ad hoc solutions.
• Long term, a solution based on a generic XML solution, perhaps not dissimilar to XML fragments, would be better.

Further concerning the designs considered in more depth after the decision, the following points were made.

• Overly complex designs will cause confusion.
• That treating all literals as XML, would create problems with legacy data, for which any solutions would be very confusing.
• Reiteration of earlier concerns of Berners-Lee and Marchiori about building XML into the heart of RDF.

An important consideration, reflected most in the comments from the Web Ontology WG and Patel-Schneider's concerns, is that unless rdf:XMLLiteral is a normal datatype with no special treatment of language, then OWL Lite and OWL DL do not support it. No version of the OWL Abstract Syntax has permitted literals other than plain literals (with or without language tags) or typed literals (without a language tag). Thus, many possible solutions would require substantive changes to OWL DL and OWL Lite.

To summarize:

@@ to be completed @@ We have received further comment concerning this aspect of our design as reflected in the 5th September 2003 Working Drafts:

• @@ from webont
• @@ any other

The Working Group did accept an @@what concession do we make - add 'at risk' part, add exit criteria@@