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RE: ISSUE-130 / ACTION-194 Come up with a proposal for conformance

From: Michael Schneider <schneid@fzi.de>
Date: Tue, 2 Sep 2008 10:48:39 +0200
Message-ID: <0EF30CAA69519C4CB91D01481AEA06A0B9868F@judith.fzi.de>
To: "Ian Horrocks" <ian.horrocks@comlab.ox.ac.uk>
Cc: "W3C OWL Working Group" <public-owl-wg@w3.org>
[related to ISSUE-130 and ISSUE-131 (Conformance and OWL RL Unification)]

Hi!

I have read the Conformance proposal at

  <http://www.w3.org/2007/OWL/wiki/Conformance>

It's a clearly written document. I have several comments/questions.

* 1.1.1. 

  """
  Any RDF/XML document is an OWL 2 Full ontology document.
  """

I suggest to replace "RDF/XML document" by "RDF document" or "RDF graph".
Whether something is a Full ontology should not depend on a specific RDF
serialization.

* 1.1.1.

   """
   An OWL 2 Full ontology document is an OWL 2 RL 
   ontology document iff it can be successfully 
   parsed using the canonical RDF parsing process 
   and the resulting ontology in the functional-style 
   syntax satisfies all the restrictions on OWL 2 RL ontologies 
   """

Now I understand that one of the purposes of the (so far) OWL RL DL syntax
is to define /syntactic/ conformance. For example, the following RDF graph
(aka OWL 2 Full ontology) is /not/ a syntactically conformant OWL RL
ontology:

  ex:C rdfs:subClassOf _:x
  _:x owl:unionOf (SEQ ex:D1 ex:D2)

because, after the reverse mapping, it would not meet the RL syntax
restrictions. I'm personally fine with this.

* 1.2.1.

  """
  An OWL 2 entailment checker takes as input 
  two OWL 2 ontology documents O1 and O2
  """

Isn't it better to talk about "two /imports-closed collections of/ OWL 2
ontology documents"?

* 1.2.1.

  """
  and either the Model-Theoretic Semantics [OWL 2 Semantics]
  or the RDF-Based Semantics [OWL 2 RDF-Based Semantics]  
  """

I just want to state that the RDF-Based Semantics is also a model-theoretic
semantics, so this is not a useful distinction criterion. 

* 1.2.1

  """
  An OWL 2 entailment checker returns one word, 
  being True, False, or Unknown.
  """

Perhaps, it's better to talk about "result" instead of "word".

* 1.2.1

  """
  An OWL 2 Full entailment checker is an OWL 2 entailment checker 
  that takes RDF/XML documents as input
  """

Again "RDF/XML". But here, one can simply write "OWL 2 Full ontology
documents", because this term has already been defined elsewhere, and it
would also be better in line with the rest of the "entailment checker"
definitions in this section.

* 1.2.1 Analog for "OWL 2 RL entailment checker". But my question is: Should
it be "OWL 2 /Full/ ontology documents" or "OWL 2 /RL/ ontology documents"?

* 1.2.1

  """
  An OWL 2 RL entailment checker
  [...] MUST return True only when O1 entails O2, 
  and it must return False 
  only when FO(O1) ? R does not entail FO(O2) 
  under the standard first-order semantics
  """

Just to be clear: This means that there can be two conformant OWL 2 RL
entailment checkers C1 and C2, where for the same query "G_L |= G_R ?" C1
answers "False" (because G_R does not follow from G_L via the rules), while
C2 answers "True" (because G_R follows from G_L via the Full semantics). I
suggest that we state it explictly that this is intended. Otherwise people
might get confused and think that this is a bug.

* 1.2.1: "terminating and complete entailment checker"

  """
  reject the input as syntactically invalid
  """

I don't understand what this means in the case of OWL RL. According to
1.1.1, RDF seems to be the reference syntax, but RDF graphs are only said to
be "RL conformant", if they can be successfully parsed into Functional Style
syntax and satisfy the RL restrictions. So I wonder whether all RDF graphs
or only those matching the RL restrictions (the "syntactically OWL RL
conformant ontology documents"!) are syntactically valid input to an OWL RL
entailment checker. Perhaps it is meant that an OWL RL entailment checker
MAY reject syntactically non-conformant OWL 2 RL documents, but if it
accepts them, then it has to provide the True/False/Unknown behavior as
stated (e.g. it must not say "True", if the OWL Full semantics do not
entail). I would like to see some clarification here. 

* 1.2.1: 

  """
  An OWL 2 entailment checker is terminating if,
  given sufficient memory resources
  """

I think that two slight clarifications are needed here:

  (1) Is by "given sufficient memory resources" meant that the amount of
memory is determined "a priorily" by the problem size? Or that memory can be
appended on demand, such as in the case of a printer running out of paper?

  (2) Definition of "completeness": Does this definition allow an input on
which the entailment checking process does not terminate? Or is the
definition of termination already part of the definition of completeness?

Best,
Michael

>-----Original Message-----
>From: Ian Horrocks
>Sent: Monday, August 25, 2008 1:27 PM
>To: public-owl-wg Group WG
>Subject: ISSUE-130 / ACTION-194 Come up with a proposal for conformance
>
>
>A draft proposal is now available in the Wiki [1]. The idea is that
>this would become the conformance section in the Test document [2].
>
>Ian
>
>[1] http://www.w3.org/2007/OWL/wiki/Conformance
>[2] http://www.w3.org/2007/OWL/wiki/Test#Conformance

--
Dipl.-Inform. Michael Schneider
FZI Forschungszentrum Informatik Karlsruhe
Abtl. Information Process Engineering (IPE)
Tel  : +49-721-9654-726
Fax  : +49-721-9654-727
Email: Michael.Schneider@fzi.de
Web  : http://www.fzi.de/ipe/eng/mitarbeiter.php?id=555

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Received on Tuesday, 2 September 2008 08:49:23 GMT

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