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Re: OWL comment - data ranges (was blank nodes in OWL DL)

From: Dave Reynolds <der@hplb.hpl.hp.com>
Date: Fri, 08 Aug 2003 10:59:47 +0100
Message-ID: <3F337493.DD2680E7@hplb.hpl.hp.com>
To: Ian Horrocks <horrocks@cs.man.ac.uk>
CC: Jim Hendler <hendler@cs.umd.edu>, public-webont-comments@w3.org

Ian,

Many thanks for your response. These do seem like plausible reasons to be
cautious and I can accept that the requirement is not strong enough to overcome
that caution. 

So "this response is satisfactory".

[Sorry for the slow reply, intervening holiday season.]

Dave

Ian Horrocks wrote:
> 
> Dave,
> 
> Thank you for your comments.
> 
> I will attempt to provide some further clarification regarding the
> WG's decision not to support naming of data ranges. The second part of
> your comment (regarding bNodes) is/will be dealt with separately.
> 
> The issue of named dataranges was discussed at the editors meeting in
> Boston. (see [1]). The following potential problems were identified:
> 
> 1. Clearly, we would like to have access in OWL to a full range of
> user-defined XML Schema datatypes derived from the built-in datatypes
> that can already be used in OWL (see [2]). This would include
> enumerated datatypes corresponding to OWL dataranges. We expect
> XML:Schema to ultimately provide a mechanism to support this. Naming
> dataranges in OWL would provide a "competing" mechanism (i.e.,
> provide an alternative way to name user defined datatypes), and this
> could interact in an undesirable way with the XML:Schema mechanism as
> and when it is introduced.
> 
> 2. OWL DL is designed so as to allow reasoning about datatypes and
> values to be cleanly separated from reasoning about classes and
> individuals. Introducing OWL names for dataranges may compromise this
> design.
> 
> It was therefore decided not to include them in the language at
> present. It may be possible to add them in the future as and when a
> thorough investigation of the issues proves that they would not have
> any adverse effects.
> 
> Please reply to this message as to whether this response is satisfactory,
> copying public-webont-wg@w3.org. Again, thank you for your comments.
> 
> Ian Horrocks
> 
> On July 23, Dave Reynolds writes:
> >
> > Jim,
> >
> > Thank you for your response to the Jena team comments on these issues.
> > Overall this response is not (yet) acceptable.
> >
> > (a) Issue: Named data ranges
> >      Your response: postpone
> >
> > We understand that the working group cannot name user-defined XSD datatypes
> > and that matter should be raised with the XML Schema working group.
> >
> > Our concern was more one of uniformity - it seems possible to have both
> > named and unnamed classes, why not data ranges? The more uniform a language
> > is, the easier the API and the fewer the support calls.
> >
> > As an example could this:
> >
> > <owl:DataRange rdf:about="#MyDR">
> >     <owl:oneOf>
> >        <rdf:List>
> >          <rdf:first>foo</rdf:first>
> >          <rdf:rest rdf:resource="&rdf;nil"/>
> >        </rdf:List>
> >     </owl:oneOf>
> > </owl:DataRange>
> >
> > be included in OWL DL, for greater uniformity with other unnamed things in
> > OWL DL (which can optionally be named).
> >
> > I confess to not understanding the research problems that you refer to as
> > being raised by naming data ranges. If there is some non-trivial problem
> > here then we certainly accept this is not a sufficiently important issue to
> > warrant additional research at this stage in the process.
> >
> > Has the WG discussed this question?
> > None of the three links you gave seemed directly related to our request:
> > [1]
> > http://www.w3.org/2001/sw/WebOnt/webont-issues.html#I5.8-Datatypes
> > [2]
> > http://www.w3.org/2001/sw/WebOnt/webont-issues.html#I4.3-Structured-Datatypes
> > [3]
> > http://lists.w3.org/Archives/Public/www-webont-wg/2002May/0040.html
> >
> >
> > (b) Issue: bNodes as object in multiple triples
> >      Your response: no change due to lack of working group consensus
> >
> > The links you gave were all to the discussion before the last call.
> > Please give an indication of the WG discussion of this issue in response
> > to last call comments.
> >
> > Specifically you said:
> > [[
> > The WG was concerned that the handling of blank nodes has not yet been
> > shown to be able to be handled in the correspondence proof of Appendix A of
> > the Semantic Document [6].
> > ]]
> > However the following messages claim to provide such a proof:
> > http://lists.w3.org/Archives/Public/www-webont-wg/2003Jun/0294
> > http://lists.w3.org/Archives/Public/www-webont-wg/2003Jun/0017
> >
> > If this proof is indeed in error an analysis demonstrating the error could
> > supply the test case that we requested.
> >    [[
> >    A rationale for not permitting this in OWL DL
> >    should be given, preferably as a test case in OWL Full
> >    showing an OWL Full non-entailment that would hold in
> >    OWL DL if such triples were permitted.
> >    ]]
> >
> >
> > (c) Issue: cycles of bNodes
> >      Your response: postpone
> >
> > Your follow up response was disappointing but acceptable.
> > http://lists.w3.org/Archives/Public/public-webont-comments/2003Jul/0045
> >
> > Dave, for the Jena team
> >
> >
> > Jim Hendler wrote:
> > >
> > > Dave-
> > >   thanks for all the comments you raised on the
> > > public-webont-comments@w3.org list.  This is the response to the
> > > remaining one:
> > >
> > > >This is a comment about blank nodes in OWL DL on behalf of the Jena team.
> > >
> > > >   - We would like it to be possible to name dataranges
> > >
> > > The Web Ontology WG discussed this issue and others to do with naming
> > > various datatypes under the issue "datatypes" which is issue 5.8 on
> > > our issues list [1] and in our issue 4.3 of "structured datatypes"
> > > [2], which included a discussion of naming datatranges raised by Ziv
> > > Hellman [3]
> > > Summarizing what can be seen in the discussions referenced there, the
> > > WG felt that
> > >    (i) we should yield to RDF Core's decisions on datatyping, and
> > >    (ii)that we shouldn't create new URIs for datatypes that might
> > > conflict with an eventual decision in the handling of XML Schema
> > > Datatypes by the XML Schema group.
> > >   In light of these considerations, the group decided to postpone
> > > issue 4.3 and not add named dataranges at this time.
> > >   The above assumes your question is specifically about complex
> > > datatypes and ranges (i.e. being able to say a teenager has as age
> > > property value between 13 and 19).  Unamed datatranges could also be
> > > asked about the ability to create datatypeProperties that are created
> > > in a manner corresponding to the creation of unnamed
> > > ObjecttypeProperties.  This was not identified by the WG as a
> > > requirement and raises some issues of a research nature as to the
> > > handling of these within the DL restrictions.
> > >
> > > - It is natural in Jena to permit the java objects
> > >    representing blank nodes which
> > >    represent descriptions and restrictions to be
> > >    used more than once, and hence as the object of
> > >    more than one triple.
> > >
> > >    A rationale for not permitting this in OWL DL
> > >    should be given, preferably as a test case in OWL Full
> > >    showing an OWL Full non-entailment that would hold in
> > >    OWL DL if such triples were permitted.
> > >    Below is an example such a test case, which we believe is an
> > >    OWL Full entailment. If on the contrary it were a
> > >    non-entailment, that would satisfy this comment.
> > >
> > > The issue of the proper treatment of blank nodes is a complex one,
> > > and has received a great deal of discussion on the WG.  Issue 5.26
> > > [4] involves many subissues involving the mapping between RDF and
> > > OWL.  Part of that discussion involved the treatment of blank nodes
> > > similar to your discussion above.  The group was unable to reach
> > > consensus on this issue, and in fact ended up closing the issue over
> > > the objection of Jeremy Carroll of Hewlett-Packard, his objection can
> > > be seen in [5].  The WG was concerned that the handling of blank
> > > nodes has not yet been shown to be able to be handled in the
> > > correspondence proof of Appendix A of the Semantic Document [6].
> > >
> > > - The RDF support within Jena permits users to:
> > >    - use annonymous nodes as the object of
> > >      more than one triple
> > >    - have cycles of anonymous nodes
> > >    While the syntactic restrictions between, for example,
> > >    unnamed individuals and descriptions are understandable,
> > >    it is not clear why OWL DL has not permitted, for example,
> > >    an unnamed individual to be the object of more than
> > >    one triple, or an unnamed individual to be the object
> > >    of a triple of which it is the subject.
> > >    Please either relax this constraint or offer a rationale.
> > >
> > > I am pasting in here the response that Peter Patel-Schneider sent to
> > > another comment raising this same issue - his answer can be seen in
> > > full in [7]
> > >
> > > The constraints on owl:equivalentClass triples can be articulated in terms
> > > of Hamilton paths in the component graphs that are created by considering
> > > only connected groups of blank nodes and named nodes that are connected to
> > > these blank nodes.  Neverthless, this is expensive to implement.
> > >
> > > The working group decided on 29 May 2003, as recorded in
> > > http://lists.w3.org/Archives/Public/www-webont-wg/2003May/0402.html, to
> > > change the mapping for owl:equivalentClass from paths to connected graphs.
> > > This should be much easier to implement.
> > >
> > > This change is reflected in the editor's draft of S&AS as of 30 May 2003,
> > > which says:
> > >
> > > --------
> > > S: EquivalentClasses(description1 ˆɬˆǬ descriptionn)
> > >
> > > T(S): T(descriptioni) owl:equivalentTo T(descriptionj) .
> > >         for all <i,j> in G where G is a set of pairs over
> > >         {1,...,n}x{1,...,n} that if interpreted as an undirected graph
> > >         forms a connected graph for --------
> > >
> > > If you'd like to review this in context, you can take a look at the
> > > editor's draft, in the the "Transformation to Triples" table at
> > > http://www-db.research.bell-labs.com/user/pfps/owl/semantics/mapping.html
> > >
> > > I hope these responses will demonstrate the rationale behind the
> > > decisions the WG has made on these issues.  We hope you can accept
> > > our postponement of one, reluctance to change our response on
> > > another, and changes made to fix the third.
> > >   -Jim Hendler
> > >   for WOWG
> > >
> > > [1] http://www.w3.org/2001/sw/WebOnt/webont-issues.html#I5.8-Datatypes
> > > [2]
> > > http://www.w3.org/2001/sw/WebOnt/webont-issues.html#I4.3-Structured-Datatypes
> > > [3] http://lists.w3.org/Archives/Public/www-webont-wg/2002May/0040.html
> > > [4]
> > > http://www.w3.org/2001/sw/WebOnt/webont-issues.html#I5.26-OWLDLSyntax
> > > [5] http://lists.w3.org/Archives/Public/www-webont-wg/2003Mar/0264.html
> > > [6]
> > > http://www.w3.org/TR/owl-semantics/proofs.html#A.1
> > > [7]
> > > http://lists.w3.org/Archives/Public/public-webont-comments/2003Jun/0022.html
> > >
> > > --
> > > Professor James Hendler                           hendler@cs.umd.edu
> > > Director, Semantic Web and Agent Technologies     301-405-2696
> > > Maryland Information and Network Dynamics Lab.    301-405-6707 (Fax)
> > > Univ of Maryland, College Park, MD 20742          *** 240-277-3388 (Cell)
> > > http://www.cs.umd.edu/users/hendler      *** NOTE CHANGED CELL NUMBER ***
> >
Received on Friday, 8 August 2003 06:01:10 GMT

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