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Re: Proposed reply to http://lists.w3.org/Archives/Public/public-webont-comments/2003May/0083.html

From: Jeremy Carroll <jjc@hplb.hpl.hp.com>
Date: Sun, 01 Jun 2003 21:18:26 +0100
Message-ID: <3EDA5F92.4090307@hplb.hpl.hp.com>
To: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>
CC: www-webont-wg@w3.org

I believe that except for the reply to *comment 3* below the commentator 
will be satisfied. With comment 3, I imagine some of the work on-going from 
the beer conversation may make the commentator happier with no direct 
change in response to this issue.

I suggest this response should be sent.

Jeremy

Peter F. Patel-Schneider wrote:

> Thank you for your comments.
> 
> 
>>This is a comment on OWL Test Cases and Last Call Comment on OWL S&AS.
>>
>>http://www.w3.org/TR/2003/WD-owl-semantics-20030331/
>>http://www.w3.org/TR/2003/WD-owl-test-20030331/
>>
>>There are five specific points at the end of this message which we ask the 
>>WG to consider.
>>
>>We implemented an OWL Syntax Checker, as defined in OWL Test Cases, based 
>>on the mapping rules in OWL S&AS.
>>
>>The approach used was to:
>>1: compute the imports closure
>>
>>2: follow the triple tables found in:
>>
>>http://lists.w3.org/Archives/Public/www-archive/2003Mar/att-0089/m
>>
>>and to work from those to iteratively classify every node in the RDF graph
>>
>>3: additional actions are used to check that restrictions, for instance, do
>>not have too many components, and that blank nodes are the object of at 
>>most one triple
>>
>>4: the syntax checker behaves incrementally in the sense that we can check
>>whether any non OWL Lite or non OWL DL constructs have been used
>>
>>5: when all the triples have been processed we have a final check for 
>>things like orphan restrictions, untyped nodes etc.
>>
>>We have slightly updated the tables.
>>(The actual table used can be found at
>>http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/jena/jena2/src/com/hp/hpl/jena
>>/ontology/tidy/Grammar.java?rev=HEAD&content-type=text/vnd.viewcvs-markup )
>>
>>
>>In this process we have not implemented the following:
>>
>>A: exact constraints concerning owl:disjointWith
>>B: exact constriants concerning owl:equivalentClass
>>C: non cyclic restricition on unnamed individuals
>>D: allowing blank restriction nodes to have class owl:Class
>>
>>C and to some extent A and D are a result of laziness; and we can imagine
>>implementing them soon.
>>
>>We believe that
>>**Comment 1**
>>+  *B* is seriously flawed in S&AS and should be fixed.
>>     (i.e. the constraints on owl:equivalentClass triples cannot
>>    even be articulated let alone implemented, let alone
>>    implemented reasonably efficiently).
>>
> 
> 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/2003Apr/0003.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 of 30 May 2003.
> 
> 
>>**Comment 2**
>>+ *A* seems unnecessarily complex
>>    Do these constraints  on owl:disjointWith have to be as complicated as
>>  they are?
>>
> 
> In the current situation it is difficult to have a different mapping for
> owl:disjointWith.  However, there may be a change to the treatment of
> unnamed classes in the mapping rules that would allow for a simpler
> treatment of owl:disjointWith.  The feasibility of this change is currently
> being investigated.
> 
> 
>>**Comment 3**
>>* *D* is clunky and we ask the group to reconsider both optional triples in
>>mapping rules such as:
>>
>>restriction(ID maxCardinality(max))
>>==>
>>_:x rdf:type owl:Restriction .
>>_:x rdf:type owl:Class . [opt]
>>_:x rdf:type rdfs:Class . [opt]
>>_:x owl:onProperty T(ID) .
>>_:x owl:maxCardinality "max"^^xsd:nonNegativeInteger .
>>
>>(the owl:Class optional triple is more problematic than the rdfs:Class, 
>>since it makes the rule on requiring explicit type for all nodes more 
>>complicated.
>>owl:Class is a possible explicit type for classID and description nodes, 
>>but not for restriction nodes). We suggest removing the optional triples 
>>from this rule, and other similar rules.
>>
> 
> The current situation is that such blank nodes must be typed with the
> appropriate class, here owl:Restriction, and can optionally be typed with
> some more-general classes, here owl:Class and rdfs:Class.  To change the
> mapping for restrictions would make their treatment needlessly different
> from the treatment of similar constructs, such as intersections and unions,
> which also have an optional rdfs:Class.
> 
> No change in response to this particular comment is anticipated.  There are
> potential changes to the treatment of such constructs that would make it
> even more desirable to allow for typing with rdfs:Class.
> 
> 
>>**Comment 4**
>>A further clunkiness was with owl:OntologyProperty.
>>Triples such as
>>owl:priorVersion rdf:type owl:OntologyProperty .
>>are permitted by the grammar iff owl:priorVersion is used somewhere else.
>>We have correctly implemented this, but it is surprising.
>>
>>We suggest either:
>>- removing the term OntologyProperty from the owl namespace and simply
>>modifiying the mapping rules that produce these triples to not do so.
>>or:
>>- allowing user defined OntologyProperty's with annotations with an 
>>abstract syntax axiom
>>
> 
> The working group decided on 29 May 2003, as recorded in 
> http://lists.w3.org/Archives/Public/www-webont-wg/2003Apr/0003.html, to
> add an axiom for ontology properties, with a treatment similar to the axiom
> for annotation properties.  This should make the situation here better.
> 
> This change will be reflected in an upcoming editor's draft of S&AS.
> Changes to other documents may also be required.
> 
> 
>>**Comment 5**
>>We did not work directly from the WD, and cannot imagine how one might 
>>easily do so. We found the tables in
>>http://lists.w3.org/Archives/Public/www-archive/2003Mar/att-0089/m
>>considerable more accessable than the mapping rules, and suggest that these
>>tables should be included in the OWL recommendation.
>>
> 
> The S&AS document is, as much as possible, a formal document giving only
> what is necessary to define the semantics of OWL.  It is thus not too
> likely that such an informative section would be attached to S&AS.
> However, there are several documents that have been produced giving a
> description of the inverse mapping, and one or more of them may be given
> some blessing by the working group.
> 
> 
> Again thank you for your comments.  We hope that you will be able to
> upgrade your OWL Syntax Checker to handle all of OWL DL and look forward to
> hearing information about future versions.
> 
> 
> Peter F. Patel-Schneider
> Bell Labs Research
> Lucent Technologies
> 
> 
Received on Sunday, 1 June 2003 16:18:50 GMT

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