RE: [RDFTM] Comments on the recent editor's draft from the ODM working group

Dear Elisa and all,

First of all, thank you very much for your comments. Please
accept my apologies (with the usual excuses) for not
replying sooner.

Since I will be proposing a formal review of the RDFTM
Guidelines at tonight's SWBPD telecon, I would like to
address your points now, albeit briefly.

| 2. Even though the RFP for the ODM called for normative
| mappings, we have concluded that normative mappings are not
| practicable, for reasons detailed in Appendix E of the
| November 2005 draft submission [1]. These reasons include
| the subtle incompatibilities among languages which are the
| subject of the recent exchange with Peter Patel-Schneider
| [2]. The ODM team therefore argues that whatever the
| eventual result of the RDFTM working group, that the product
| be seen as informative, rather than normative.

We agree. The guidelines we are producing can only be just
that -- guidelines. There will always be alternative ways to
approach the problem which may be better suited in some
applications. However, we feel that there is also a need for
community consensus on an approach that can also provide a
degree of interoperability across applications. This
approach will certainly not be mandated in any way; your
recommendation to make the product informative rather than
normative accords with this.

| 3. The ODM team is happy with the concept of a semantic
| mapping. The ODM mappings are also semantic. However, we
| take issue with the choice of guided rather than unguided
| mappings. Of course unguided mappings are underdetermined.
| That is one of the reasons for the decision that the ODM
| mappings be informative only. We agree that in practice a
| mapping will need to be guided. Our objection is that the
| context-free guidance proposed for the RDFTM will likely
| have limited utility. Reasons for this objection are
| detailed below.

Our position on this is that guided translations provide
much better results than unguided translations and are
therefore to be preferred. However, we have always intended
to address both guided and unguided translations. Our
decision to focus on guided was in the first draft of the
Guidelines was based on the fact that they are simpler. But
now we have most of the guidelines for guided translations
in place, it turns out that there is not much more to do in
order to support unguided translations as well. Our current
plan is therefore to address both, provided our time
constraints permit this.

| [Justification for focusing on unguided mappings omitted.]
|
| 3.3 The ODM team therefore argues that the RDFTM describe
| the unguided mappings with their indeterminacies, then
| provide some guidance using a non-normative light-weight
| mechanism.

Your point is very well taken. However, we have deliberately
chosen to avoid the issue of transformations between
ontologies and vocabularies. Unfortunately this was not
stated clearly enough in our first draft; that has now been
rectified.

Like you, we believe that many applications will need to be
able to transform between different ontologies, but this
problem is not limited to RDF/Topic Maps interoperability.
It therefore seems wrong for us to cater for this in any way
in our Guidelines. We prefer to address a scenario in which
any transformations that are required are performed prior to
and subsequent to the actually exchange of data between RDF
and Topic Maps based systems. Given this approach, we think
we *can* provide guidelines for the actual interchange of
data that are useful in and of themselves, especially if
guidance is included. Guided translations are therefore seen
as being of greater practical benefit than unguided
translations.

| 4. From the perspective of OWL, the annotation method
| advocated in RDFTM for RDF is the use of properties whose
| domain is other properties. The annotated ontology is
| therefore OWL Full. As noted in the RDFTM, OWL has a
| lighter-weight mechanism compatible with OWL DL, namely
| annotation properties. Although these properties cannot be
| used for property axioms, they can be used by the software
| implementing particular mapping languages.

We agree and we would like feedback from the rest of the
Working Group as to whether we should provide an alternative
mechanism that does not necessarily lead to OWL Full.

| 5. The RDFTM includes a consideration of a number of untyped
| topic map constructs: associations, occurrences, association
| roles. The working party should know that in TMDM 2005-12-16
| (and in the earlier 2005-10-28) all these constructs are
| required to be typed.

This is correct. However, earlier versions of the Topic Maps
standard do allow untyped topic map constructs and therefore
this issue needs at least to be addressed, if not actually
catered for.

| 6. Note that although RDF does not have a container
| construct like Topic Map, OWL does. An OWL ontology, as
| distinct from the resource owl:Ontology, contains the
| statements defining it, providing context for the
| restrictions in OWL DL and OWL Lite.

We assume that your point here is that this might be a way
to handle reified Topic Maps. You may well be correct. We
are currently looking into this.

Thanks once again for your comments and for offering to do a
formal review of the Guidelines.

Best regards,

Steve

--
Steve Pepper <pepper@ontopia.net>
Chief Strategy Officer, Ontopia
Convenor, ISO/IEC JTC 1/SC 34/WG 3
Editor, XTM (XML Topic Maps 1.0)


  -----Original Message-----
  From: public-swbp-wg-request@w3.org [mailto:public-swbp-wg-request@w3.org]On Behalf Of Elisa F. Kendall
  Sent: 17. februar 2006 03:13
  To: Steve Pepper
  Cc: swbp; Bob Colomb; Evan Wallace; Christopher Welty; Guo Tong Xie; 'Yue Pan'
  Subject: [RDFTM] Comments on the recent editor's draft from the ODM working group


  Steve and all,

  Because the issues that RDFTM is attempting to address are also relevant to our work on ODM,
  we felt that it was important for us to review and comment on this document.  As you and Lars
  may recall, Lewis Hart, formerly with AT&T Government Solutions, did much of the original work
  on our metamodel for Topic Maps.  More recently, though, Bob Colomb has taken on much of this
  work, with significant input from the ISO TM community, particularly in Japan.

  We discussed the issues during our conference call this week, summarized as follows.

  1. The OMG ODM (Ontology Development Metamodel) group has been working on mapping among various ontology
representation languages for nearly two years. This work includes mapping between Topic Maps and OWL, so the RDFTM
proposals impact the ODM.

  2. Even though the RFP for the ODM called for normative mappings, we have concluded that normative mappings are not
practicable, for reasons detailed in Appendix E of the November 2005 draft submission [1]. These reasons include the
subtle incompatibilities among languages which are the subject of the recent exchange with Peter Patel-Schneider [2].
The ODM team therefore argues that whatever the eventual result of the RDFTM working group, that the product be seen as
informative, rather than normative.

  3. The ODM team is happy with the concept of a semantic mapping. The ODM mappings are also semantic. However, we take
issue with the choice of guided rather than unguided mappings. Of course unguided mappings are underdetermined. That is
one of the reasons for the decision that the ODM mappings be informative only. We agree that in practice a mapping will
need to be guided. Our objection is that the context-free guidance proposed for the RDFTM will likely have limited
utility. Reasons for this objection are detailed below.

  3.1 Using terminology from our usage scenarios analysis in Chapter 7 (table 7) of [1], there are at least two reasons
why one might want to map an ontology from one representation to another. One is that an ontology in one representation
describes a legacy system, and that the original ontology, part, or all of the legacy system is being migrated to
another representation. This would be typical of information systems development applications.  Here, the context for
guidance is dependent on the aims of the specific project, which could easily differ from the generic choices included
in the RDFTM.  Further, under such circumstances it would be unlikely that the continuing development would wish to
maintain backwards compatibility with the legacy source.  This is partly because the subtle differences in
expressibility make this difficult, and partly a cost measure.  So for this kind of application, the RDFTM guidance is
very likely to be too generic, and the recommendation for annotation of the target unlikely to be maintained in
downstream development.

  3.2 Another use case considered requirements for continuing interoperability in run-time interoperation applications
like e-commerce exchanges and application development applications involving re-use of a standard domain ontology like
Gruber's Engineering Mathematics ontology or the Foundational Model of Anatomy. Here, the context for any mappings is
the specific ontology governing the application. There are many different methods of representing ontologies, so it is
possible that the governing ontology would be represented in a language other than RDF or TM. In particular, neither RDF
nor TM are used for representing either the Engineering Mathematics or Foundational Model of Anatomy ontologies. The
former was developed in Ontolingua and the latter in a frame-based language. So a project to develop an application in
this space in either RDF or TM would have to make compromises and design decisions different from the guidance proposed
in the RDFTM.

  3.3 The ODM team therefore argues that the RDFTM describe the unguided mappings with their indeterminacies, then
provide some guidance using a non-normative light-weight mechanism.

  4. From the perspective of OWL, the annotation method advocated in RDFTM for RDF is the use of properties whose domain
is other properties. The annotated ontology is therefore OWL Full. As noted in the RDFTM, OWL has a lighter-weight
mechanism compatible with OWL DL, namely annotation properties. Although these properties cannot be used for property
axioms, they can be used by the software implementing particular mapping languages.

  5. The RDFTM includes a consideration of a number of untyped topic map constructs: associations, occurrences,
association roles. The working party should know that in TMDM 2005-12-16 (and in the earlier 2005-10-28) all these
constructs are required to be typed.

  6. Note that although RDF does not have a container construct like Topic Map, OWL does.  An OWL ontology, as distinct
from the resource owl:Ontology, contains the statements defining it, providing context for the restrictions in OWL DL
and OWL Lite.

  Thanks and best regards,

  Elisa

  [1] http://www.omg.org/cgi-bin/doc?ad/05-09-08
  [2]http://lists.w3.org/Archives/Public/public-swbp-wg/2006Feb/0099.html