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RE: Response to Andy Seaborne's comments on rdf:text

From: Seaborne, Andy <andy.seaborne@hp.com>
Date: Mon, 19 Jan 2009 14:07:49 +0000
To: Jie Bao <baojie@cs.rpi.edu>
CC: Sandro Hawke <sandro@w3.org>, Axel Polleres <axel.polleres@deri.org>, Boris Motik <boris.motik@comlab.ox.ac.uk>, W3C OWL Working Group <public-owl-wg@w3.org>, "Reynolds, Dave Everett" <dave.reynolds@hp.com>
Message-ID: <B6CF1054FDC8B845BF93A6645D19BEA35621489BE7@GVW1118EXC.americas.hpqcorp.net>
> -----Original Message-----
> From: baojie@gmail.com [mailto:baojie@gmail.com] On Behalf Of Jie Bao
> Sent: 14 January 2009 17:22
> To: Seaborne, Andy
> Cc: Sandro Hawke; Axel Polleres; Boris Motik; W3C OWL Working Group
> Subject: Response to Andy Seaborne's comments on rdf:text
> 
> Hi Andy
> 
> Thank you for your comment [1] on rdf:text [2]. Here is some my
> personal opinion on the issues you described. Other authors of the
> document may have further comments.

Noted - your message was not a formal working group response.

> 
> Summary: In short, I believe your concern in mainly on the
> compatibility between rdf:text and the current specifications
> including RDF and SPARQL. I agree that rdf:text should not change the
> current specifications, explicitly or implied, nor have an impact on
> the behavior of existing tools that are designed to handle RDF. The
> wording of rdf:text should be changed to make this position clear. On
> the other hand, other syntaxes of OWL and RIF, without legacy issues,
> should be required to use rdf:text.

In discussions on public-rdf-text, it's clear that it was not the intention behind the rdf:text draft to change RDF.  Our issues stem from the fact that the text of the document, not the intent, can create visible change in RDF (as we jointly established in discussions there).

> ===========
> 
> "Issue 1: systems that do understand rdf:text may represent
> information in RDF in two different ways that other RDF systems not
> upgraded to rdf:text will interpret in two different ways."
> 
> I agree with your proposal that an RDF/XML implementation must
> abbreviate "xyz@lang"^^rdf:text into "xyz"@lang. In fact, Sandro had
> similar thoughts in a previous mail [3], which matches my belief so
> well that I quote it below

Just to be clear here [3] suggests using "SHOULD NOT" 
"""
rdf:text SHOULD NOT be used in
any RDF syntax which has built-in support for language tagging
"""
And in our suggestions, it is "MUST NOT".

Our aim is that rdf:text does not appear in RDF serialized forms anywhere.  We can do this for the case of OWL/RIF system => RDF => OWL/RIF system, where the original data originates outside of RDF, with the changes we suggested.

The other case of RDF=>OWL/RIF system=>RDF, where the original data is created in RDF, is more problematic and can only rely on the "SHOULD" provision of introducing new vocabulary into the RDF namespace.

A statement in the rdf:text document to stress that rdf:text SHOULD NOT be used in RDF data would be helpful.

> 
> "For simplicity of implementation, I think RDF serializations should
> mandate use of one style of language tagging or the other.  In order to
> handle legacy syntaxes which were created before rdf:text and so could
> not pick, I think we should probably say rdf:text SHOULD NOT be used in
> any RDF syntax which has built-in support for language tagging (in order
> to avoid all the problems you name, below).
> 
> That is, in RDF/XML, N-Triples, N3, and Turtle, one SHOULD NOT use
> rdf:text.  (Happily, this aligns with rdf-syntax saying "Any other names
> are not defined and SHOULD generate a warning when encountered, but
> should otherwise behave normally.")  Meanwhile, the various RIF syntaxes
> and the newer OWL syntaxes do not directly support language tagging, so
> one has to use rdf:text.  Perhaps a Turtle 1.1 would remove type-a
> language tagging and mandate rdf:text instead.  Similarly, APIs are free
> to pick one or the other (or some other, equivalent) approach, but
> should probably just provide one, and certainly not distinguish between
> the two."

We don't support the sentiment of that rdf:text is a replacement in RDF and that other forms are legacy. This has not been discussed in the full semantic web community.

This could all be avoided if there were a direct mapping from "text"@lang to the value space, just using rdf:text as the URI for the datatype but not coupled to the lexical presentation.  In that case, there is no need for rdf:text in abstract syntax of RDF and the special rules on interpretation of it's lexical form.
 
> 
> Thus, I propose to
> * make the two changes you suggested for this issue

Thank you.

> * add the following text to the end of the 1st paragraph of section 3.
> 
> <A language syntax that does not directly support language tagging by
> RDF's plain literal with language tags, including but not necessarily
> limited to other OWL and RIF syntaxes, MUST use rdf:text as the
> datatype for internationalized strings>

We do not agree with this.  It is speculation on what some future language goals might be or what the experience with rdf:text will be.  We also note that language tags in RDF come form the use of xml:lang in XML so this text would need to apply to XML syntaxes as well.


By the way: 
I don't know if anyone else has pointed this out but internationalized text in RDF includes XML literals.  Language tags are only part of the picture and incomplete (for bidi text). 

> =================
> 
> "Issue 2: The treatment of xs:string is at odds with the current RDF
> specifications."
> 
> I agree that in RDF the equivalence of "xyz" and "xyz"^^xs:string is
> semantically, but syntactical. Thus, the abbreviation suggested in the
> rdf:text spec should not imply that it introduces this change to the
> RDF syntax spec. 

Agreed - the way to avoid a change is to have only one way of abbreviating "text"^^rdf:text.  If there are two, then observations without the entailments from XSD1a and XSD1b will see a difference.

> In stead, in addition to your suggestions, we can add
> a note in 3.2 saying that
> 
> <Note: the abbreviation of a literal of datatype xs:string is a
> consequence of the semantic equivalence of the abbreviated and
> original forms of the literal, as described by the RDF semantics [RDF
> Semantics]. >

I don't understand the meaning here - abbreviation is the process of transforming literals of datatype rdf:text isn't it?  I assume in OWL that no literals of datatype xs:string would be present as they have a rdf:text form.  Or can there be two representations?

Read without qualification, your text implies "text"^^xs:string be transformed to "text" which is observable in RDF.

I have just noticed:
Sec 3.2 : rdf:text doc:
"""
form "text"^^xs:string can be abbreviated as "text".
"""
From 
[[
This specification defines a convenient representation for rdf:text and xs:string literals. In particular, literals of the form "text@lang"^^rdf:text where "lang" is not empty can be abbreviated as "text"@lang; furthermore, literals of the form "text"^^xs:string can be abbreviated as "text".
]]

Is this a typo?  

From context, having just mentioned literals of form "text@lang"^^rdf:text, and lang not empty, did you mean "text@"^^rdf:text where lang is empty i.e. pairs ("text" , "" ).   Otherwise the text does not cover the ("text" , "" ) case.

"text"^^xs:string  and "text" are not interchange in RDF.   Feedback to us is that application developers editing data expect their original form to be preserved, not converted from xs:string to plain literal or vice versa, even if semantically equivalent.

(Personal note: the interactions of plain literals without language tag and literals of datatype xs:string have been a source of confusion to real applications and their developers - my experience is that the design in the RDF specs is less than ideal but it is something we have to work with especially given the significant amount of deployed RDF applications.)

> 
> Please let me know if the suggested changes sufficiently address your
> concerns. I'm happy to further exchange ideas with you, and thank
> again for your constructive comments.

We believe our changes are sufficient.  The additional text you suggest goes beyond that and we will review it - maybe that would be better in context of the next revision of the document.

If it would be helpful and you would like us to look at an unpublished draft, maybe as it is finalized on the wiki, then do let us know when it is in a suitable state to review.

	Andy

> 
> [1] http://lists.w3.org/Archives/Public/public-owl-

> comments/2009Jan/0001.html
> [2] http://www.w3.org/TR/2008/WD-rdf-text-20081202/

> [3] http://lists.w3.org/Archives/Public/public-rdf-

> text/2008OctDec/0028.html
> 
> --
> Jie
> http://www.cs.rpi.edu/~baojie

Received on Monday, 19 January 2009 14:09:07 GMT

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