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Re: OWL comment - blank nodes in OWL DL

From: Dave Reynolds <der@hplb.hpl.hp.com>
Date: Wed, 23 Jul 2003 10:21:10 +0100
Message-ID: <3F1E5386.A80B1974@hplb.hpl.hp.com>
To: Jim Hendler <hendler@cs.umd.edu>
CC: public-webont-comments@w3.org


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">
         <rdf:rest rdf:resource="&rdf;nil"/>

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:

(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:

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.

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 Wednesday, 23 July 2003 05:21:40 UTC

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