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[LC Response] To Jos de Bruijn Re: a few comments about the OWL 2 drafts

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Wed, 18 Mar 2009 14:53:31 -0400 (EDT)
Message-Id: <20090318.145331.41177262.pfps@research.bell-labs.com>
To: debruijn@inf.unibz.it
Cc: public-owl-comments@w3.org
Dear Jos,

Thank you for your message
<http://lists.w3.org/Archives/Public/public-owl-comments/2009Jan/0024.html>
on the OWL 2 Web Ontology Language last call drafts.


Anchors have been added in many places, feel free to ask for more, as
adding anchors changes neither the form nor the meaning of the documents.
The general form of the anchors are def_<term_with_underscores>, but
this was not feasible in all cases.   The documents provide anchors for
each section which can also be used in other documents.

Diffs are not provided here for all changes, as the addition of anchors
may have been interspersed with other work on the documents. 

Initial diffs for Direct Semantics can be found at:
http://www.w3.org/2007/OWL/wiki/index.php?title=Direct_Semantics&diff=17912&oldid=17717
Initial diffs for Syntax can be found at:
http://www.w3.org/2007/OWL/wiki/index.php?title=Syntax&diff=17910&oldid=17665


Structural Specification and Functional Syntax document:

The discussion of datatype maps in Section 4 of the Specification
document is not a formal one, it concentrates on those parts of datatype
maps that are needed for the syntax, deferring formal discussion to
Section 2 of the Direct Semantics document.  It is thus appropriate that
Section 4 of the Syntax document does not explicitly call out the
semantic mappings that are part of datatype maps, only alluding to their
presence.

The precisionDecimal datatype of XML Schema perhaps could have been
included in OWL 2.  However, the definition of equality and order on
precisionDecimal does not appear to be what would be desired in a
representational setting (which would instead be based on viewing
elements of the datatype as ranges of numbers).  

Due to several comments and implementation experience, hexBinary and
base64Binary now have disjoint value spaces, so there is no difference
from XML Schema.  This is a change to OWL 2.

The OWL WG agrees that PNG would be preferable to GIF.  The WG expects
to convert the GIF figures to PNG at the time of next publication.


Direct Semantics document:

Full linking from the Direct Semantics is a major task, which would, for
example, include linking syntax.  Links have been added in the
Vocabulary section. The diffs are
http://www.w3.org/2007/OWL/wiki/index.php?title=Direct_Semantics&diff=17913&oldid=17912

The definition for datatype maps in Direct Semantics extends datatype
maps from RDF Semantics, in particular for facets.  

The wording "satisfies appropriate conditions listed in the following
sections" in Section 2.3 has been changed to "satisfies the condition in
the tables below for the axiom". The diffs are
http://www.w3.org/2007/OWL/wiki/index.php?title=Direct_Semantics&diff=17914&oldid=17913

Axiom closure is defined in Syntax.  A link to the definition has been
added where the term is used. The diffs are
http://www.w3.org/2007/OWL/wiki/index.php?title=Direct_Semantics&diff=17915&oldid=17914

If the document was being rewritten from scratch, the subsections of
section 2.3 might not be needed, but they seem to be innocuous and will
stay for now.

The definition of axiom closure from Syntax includes "renaming apart" so
the parentheses in 2.3.6 are appropriate.

Section 2.5 now includes a standard definition for variables and the
definition of Boolean Query Answering notes that quantification needs to
be considered.  The diffs are 
http://www.w3.org/2007/OWL/wiki/index.php?title=Direct_Semantics&diff=17918&oldid=17915

In Section 3 "is is" has been replaced by "is".  No diffs are available
for this interesting change.

The second edition of the DL handbook is now referenced.  Again no diffs
are available for this useful change.

"I" is uniformly used as a signal for an interpretation, instead of
sometimes Int and sometimes I.  The diffs are
http://www.w3.org/2007/OWL/wiki/index.php?title=Direct_Semantics&diff=17932&oldid=17923

The above changes are all editorial.


Profiles document:

As stated in the document, OWL 2 RL is designed for easy and efficient
implementation using existing forward-chaining rule systems.  Adding
owl:Thing or reflexive object properties needs rules that operate over
all individuals, which goes against efficiency, and may not even be
possible in some rule systems.  Similarly, most rule systems are
designed for positive ground facts which dictates against allowing
negative property assertions.

The phrase "General concepts of the language" has been replaced by an
explicit pointer to Section 13.1 of Syntax. This change was done in two
phases: 
http://www.w3.org/2007/OWL/wiki/index.php?title=Profiles&diff=prev&oldid=19186
and
http://www.w3.org/2007/OWL/wiki/index.php?title=Profiles&diff=19552&oldid=19193

The non-terminal subObjectPropertyExpressions is used uniformly
throughout the document set, but it really should be
subObjectPropertyExpression.  This is only a change to a non-terminal in
the grammar, which is an editorial change.  The diffs are:
http://www.w3.org/2007/OWL/wiki/index.php?title=Profiles&diff=18708&oldid=18687
http://www.w3.org/2007/OWL/wiki/index.php?title=Syntax&diff=18707&oldid=18533

The above changes are all editorial.


RDF-Based Semantics document:

As a general note, please be aware that the RDF-Based Semantics is not
yet a Last Call working draft, and it has received considerable editing
since the last publication in December.

It is indeed intended to have the same set of datatypes and facets in
the RDF-Based Semantics spec as in the Structural Specification. The
working group agrees that this should be more explicitly stated, since
it does not easily follow from the text in the published working
draft. Therefore, the working group plans to add clarifying text in the
next published working draft. 

Note that the OWL 2 RDF-Based Semantics aims for full compatibility with
the semantics defined in the RDF Semantics specification. The
semantics there already provides notions of datatypes and datatype maps,
and defines certain semantic conditions for them. In particular, as for
OWL 1 Full, the central definition of an OWL 2 Full interpretation
provided in the RDF-Based Semantics document builds on top of the
definition of a so called "D-interpretation", as defined in the RDF
Semantics specification, and by this the existing definitions of
datatypes and datatype maps from the RDF Semantics specification are
reused. 

Further, since OWL 2 provides for the new concept of datatype facets,
the definition of a datatype, as given in the RDF Semantics
specification, has been extended by the notion of a facet
space. Extending the definition of a datatype is explicitly permitted by
the RDF Semantics specification (see section 5.1 of [2]). 

Nevertheless, it is true that the different concepts used in the
definition of the extension for facets did not well match the concepts
used in the Direct Semantics specification in the last published working
draft. This is currently under revision, and the final outcome will be
that the different concepts are compatible with each other in that the
different notions of datatype maps can be easily transformed in each
other. 

Thank you for pointing out the typographical error "an OWL", it will be
fixed in the next publication. 

The purpose of Section 6 of the RDF Semantics is to show how the two
semantics of OWL 2, the RDF-Based Semantics and the Direct Semantics,
relate to each other. There is corresponding material in the OWL 1
recommendations.  Be informed that at the time of the last publication,
this section was in a very early and incomplete state. A final and much
enhanced version of this section is planned for the next publication. 


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Regards,
Peter F. Patel-Schneider
Michael Schneider
on behalf of the W3C OWL Working Group 
Received on Wednesday, 18 March 2009 18:52:35 GMT

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