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Jena comment: Syntax Checker Implementation Report]

From: Jeremy Carroll <jjc@hplb.hpl.hp.com>
Date: Mon, 12 May 2003 10:29:39 +0100
Message-ID: <3EBF6983.1030302@hplb.hpl.hp.com>
To: WebOnt WG <www-webont-wg@w3.org>


The following comment, which I drafted, was approved by the Jena team, and
then I was not sure where to send it on Friday, and the task got lost.

Jim

do you want to:
- move this to public-webont-comments yourself
- have me post it there on behalf of Jena team
- just work with the comment in this list
- have some other member of the Jena team post it to the comments list

Jeremy


[[[

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).

**Comment 2**
+ *A* seems unnecessarily complex
    Do these constraints  on owl:disjointWith have to be as complicated as
  they are?

**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.

**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

**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.

]]]
Received on Monday, 12 May 2003 05:30:38 GMT

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