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. The one that appears closest to the position of the I18N group was that to unify plain and XML literals.

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.

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

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

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:

untyped literal
typed literal
Wrapped normal
typed literal
typed literal
no wrapping
All literals
are XML
use a generic
datatyping mechanism
No No Yes Yes N/A
XML syntax ...
arbitrary choice
No No Yes Yes NO
[permit] non-built-in
datatype [like]
No No Yes Yes No
[avoid] an
RDF-specific solution
[to the problem of]
XML [...] context
Yes Yes No Yes ?
[avoid] smack[ing]
of being a hack
Yes No No Yes No
xml:lang [is]
Yes Yes Yes No Yes
Works with OWL
Candidate Rec
No No Yes Yes No
Legacy plain literals
are OK
Yes Yes Yes Yes No
Legacy XML literals
are OK
No No No No No

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

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