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Re: comment - RDFTM: Survey of Interoperability Proposals

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Wed, 23 Mar 2005 21:01:52 -0500 (EST)
Message-Id: <20050323.210152.49682207.pfps@research.bell-labs.com>
To: pepper@ontopia.net
Cc: public-swbp-wg@w3.org

From: "Steve Pepper" <pepper@ontopia.net>
Subject: RE: comment - RDFTM: Survey of Interoperability Proposals
Date: Wed, 23 Mar 2005 19:04:05 +0100

> * Peter Patel-Scheider
> 
> | This is collection of comments on RDFTM: Survey of Interoperability
> | Proposals http://www.w3.org/2001/sw/BestPractices/RDFTM/survey-2005-02-24.
> | 
> | First, however, a disclaimer:  I am a long-time skeptic of the entire Topic
> | Maps paradigm.  I have tried several times to determine whether there is
> | something interesting in Topic Maps and each time I have been unsuccessful.
> | My skepticism colors many of these comments.
> 
> Thank you for stating this up front.
> 
> | The first problem that I see with the document is that it doesn't define
> | the two paradigms.  There are no references to any of the defining RDF
> | documents.  There are several references that could be considered to be
> | defining Topic Maps - however, these do not show up until very late in the
> | text and thus cannot be considered to be a definition for the purposes of
> | this document.
> 
> All relevant defining documents (i.e., RDF Concepts, RDF Schema, OWL,
> and RDF Primer) are now referenced in Section 1, Introduction.

I note that RDF Semantics is not referenced anywhere in the documents.  I
find this very strange as RDF Semantics provides the formal basis for RDF.

I don't see that RDF Concepts has anything to do with a formal model of
RDF, as opposed to what is implied in Section 4.  Similarly, I don't see
any causal relationship from OWL to a formal model for RDF.  Certainly the
OWL Guide does not provide anything that can be used as a formal model for
RDF.

> | This lack of a definition matters for reasons from both the RDF and the
> | Topic Maps side.  RDF has undergone a significant change in the last few
> | years from a pre-theoretic language with no firm foundation (see Resource
> | Description Framework (RDF) Model and Syntax Specification
> | http://www.w3.org/TR/1999/REC-rdf-syntax-19990222/) to a full-fledged logic
> | (see RDF Semantics http://www.w3.org/TR/rdf-mt/).  Which version of RDF is
> | meant in the document?  Which version of RDF to the interoperability
> | proposals refer to?  As well, what is the place of RDFS in the document?
> | Is it included?  Is it excluded?  
> 
> It is now clearly stated
> 
> 1) that most of the proposals in the Survey were written before the 2004
>    finalization of the above-mentioned documents; and
> 
> 2) the extent to which RDF Schema and OWL are considered relevant to the
>    Survey and the further work of the RDFTM task force. 

However, the document still states that correspondence between data models
is the end point of the exercise.  I believe that this is wrong at least
for RDF (and maybe even for Topic Maps) and that the correspondence on the
RDF side should be to sets of models on the RDF side (or, more-or-less
equivalently, to RDF graphs modulo equivalence.

Now one might argue that the correct end point on the RDF side is indeed
just data, but this is an argument that at least needs to be made - just
stating the end point is not sufficient. 

[...]

> | The second problem is that many of the interoperability proposals predate
> | the finalization of the RDF Semantics.  Their current applicability is thus
> | very suspect.  The document needs to carefully consider this aspect of each
> | proposal.
> 
> Noted.

I do not believe that sufficient attention has been made to this point.
The changes to RDF, in particular, may mean that there is nothing that can
be salvaged from approaches that used previous versions of RDF.

As well, simply putting RDF and Topic Maps on a firm footing is insufficent
to ensure interoperability, as opposed to the sentiment from Section 4

	Now that these formal models exist, it should be possible to define
	complete and correct mappings at either the object or the semantic
	level.

> | The third problem is that RDF and Topic Maps belong to different
> | categories, at least so far as I can determine.  RDF is now a
> | formally-specified logic with a model-theoretic semantics.  Topic Maps is
> | not.  This difference matters, and needs to be taken into account in every
> | discussion of the relationship between RDF and Topic Maps.  At best, there
> | needs to be some way to determine that the interoperability proposals
> | preserve logical equivalence on the RDF side.  At worst, there is no point
> | in doing any mappings, as RDF and Topic Maps are simply incomparable.  [For
> | indications why this might be the case, consider that Topic Map merging as
> | defined in http://www.isotopicmaps.org/sam/sam-model/ is claimed to not
> | remove all redundant information in a topic map.  How then can it be
> | determined whether a mapping is reasonable?  As well, the procedure defined
> | therein does not terminate.]
> 
> RDF and Topic Maps may well belong to different categories (that would be
> in the eye of the categorizer). 

> Nevertheless, the SWBPD has determined
> that there is both a need and a potential for achieving some level of
> interoperability at the data level. 

I would like to see evidence for this specific point.  I don't see it in
the task force description at
	http://www.w3.org/2001/sw/BestPractices/RDFTM/.

> That does not mean that either RDF or
> Topic Maps will ever be able to replace the other: In that sense they may
> be "incomparable" It does however mean that there can be some benefit to
> be derived from being able to move data between the two. My personal
> experience tells me that the market certainly thinks so.

It is possible that there may be value to be obtained from moving
information between RDF (or RDFS or OWL) and Topic Maps.  However, the
Survey embodies a particular view of how this is to be done, which may
result in better methods for transfering information not being
appropriately investigated.

[...]

> Best regards,
> 
> Steve

Peter F. Patel-Schneider
Bell Labs Research
Received on Thursday, 24 March 2005 02:02:06 UTC

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