RE: ISSUE-104: Several issues with the current treatment of disallowed vocabulary

Hi Boris!

To (B): You are perfectly right! I simply overlooked this problem. So, yes,
the disallowed vocabulary is probably best placed in the DL-syntax document.
A small note in the RDF mapping, which cites the DL-syntax, might be of
value, however. Note that in the AS&S, the disallowed vocabulary was placed
in the RDF mapping, so people might search for it.

To (A) and (C): It's easy to come up with a list of vocabulary, which leads
to backwards-compatibility problems, but I won't find the time to do this
tonight. One simply has to compare the set of all URIs in the RDF(S) and
OWL(1) namespace with the list given in the AS&S. Every URI, which is not
listed in the AS&S, may be used in OWL 1 DL documents. Which of these URIs
are useful is another question, though. I am going to check this (later) and
come up with a suggestion for discussion.

Cheers,
Michael

>-----Original Message-----
>From: Boris Motik [mailto:boris.motik@comlab.ox.ac.uk]
>Sent: Wednesday, June 04, 2008 10:59 AM
>To: Michael Schneider; public-owl-wg@w3.org
>Subject: RE: ISSUE-104: Several issues with the current treatment of
>disallowed vocabulary
>
>Hello,
>
>I disagree with (B). If we were to go with this suggestion, then we
>would have two different types of OWL 2 DL ontologies:
>
>- We'd have OWL 2 DL ontologies as specified in the SS document. These
>might actually use the reserved vocabulary, so they wouldn't
>be serializable into RDF.
>- We'd have OWL 2 DL ontologies that do not use the reserved vocabulary
>and therefore are serializable into RDF.
>
>All of this seems unnecessarily complex and makes the whole story harder
>for people to follow. We need one place to say what
>constitutes a valid OWL 2 DL ontology, and this definition should be in
>one place and not spread across the documents. True, we
>might allow using the reserved vocabulary if we are not storing an
>ontology into RDF, but do we really need this/care about it? This
>is particularly true if we work under the quite common assumption that
>RDF is the main syntax of OWL 2. It is therefore much more
>coherent to just define everything in one place and not bother with the
>exceptions.
>
>
>
>Also, I am not sure about (C). The whole idea of the reserved vocabulary
>is that it should be reserved -- that is, it is the
>vocabulary that is given precise meaning by RDF and/or OWL semantics, so
>the users should "keep their hands off of it". It might be
>the case that nothing bad happens even if we allow the usage of some
>particular URI, but why would we bother? What is the benefit of
>doing this? Users will be more likely to clearly understand a statement
>"anything with the URI owl:* is reserved and you shouldn't
>use it" than "this, that and the other is reserved, but those things are
>OK".
>
>
>I accept that (A) might be an issue. Before we decide on the way
>forward, however, I would appreciate it is you could provide us
>with a list of vocabulary that actually causes problems.
>
>Regards,
>
>	Boris
>
>
>
>> -----Original Message-----
>> From: Michael Schneider [mailto:schneid@fzi.de]
>> Sent: 03 June 2008 21:38
>> To: public-owl-wg@w3.org
>> Cc: Boris Motik
>> Subject: ISSUE-104: Several issues with the current treatment of
>disallowed vocabulary
>>
>> Hi!
>>
>> At the last telco, Boris (cc'ed) told me that ISSUE-104 (disallowed
>> vocabulary) is probably moot, since there is already a notion of a
>"reserved
>> vocabulary" in sec. 2.2 of the DL-Syntax document [1].
>>
>> I have read this section in the meanwhile, and have found three
>issues, which
>> still remain. So I disagree that this issue is already resolved. The
>three
>> issues are pretty independent of each other, and can therefore be
>discussed
>> separately.
>>
>> I claim:
>>
>>   (A) Backwards Compatibility:
>>       The set of disallowed vocabulary covers URIs,
>>       which were allowed to be used in OWL 1 DL.
>>       Hence, we have a backwards-compatibility issue.
>>
>>   (B) Responsibility:
>>       The disallowed vocabulary should be in the
>>       RDF mapping, not in the DL-syntax document.
>>
>>   (C) Relaxation:
>>       It seems to be possible that a fraction of the
>>       previously disallowed vocabulary can be allowed
>>       to be used in OWL 2 DL.
>>
>> I will provide a more detailed argumentation for all these claims
>below.
>>
>> (A): Backwards compatibility
>> ----------------------------
>>
>> The current disallowed (or "reserved") vocabulary is defined to be the
>set of
>> all URIs within the RDF(S) and OWL namespace (and some additional).
>But in OWL
>> 1 DL, according to [2], there existed some URIs from these namespaces,
>which
>> were actually allowed to be used in OWL DL ontologies. An example is
>the RDF
>> reification vocabulary.
>>
>> ! Proposal: Explicitly itemize the disallowed URIs, just as in the old
>AS&S.
>>
>> (B): Responsibility
>> -------------------
>>
>> Technically, it doesn't matter whether the disallowed vocabulary is
>presented
>> in the DL syntax or in the RDF mapping. However, there is a question
>of
>> responsibility. I claim that having it in the DL syntax does not make
>much
>> sense, while it there is a good reason to have it in the RDF mapping.
>>
>> >From the point of view of OWL 2 DL and its Functional Syntax, there
>is no
>> reason to /not/ allow, for example, the use of the URI
>'rdfs:subClassOf' at,
>> for example, any position within a class assertion. This URI is
>neither used
>> within the Functional Syntax itself, nor does it have a special
>meaning in the
>> DL semantics.
>>
>> As an easy check, imagine that there was no RDF syntax for OWL DL.
>This would
>> have no technical consequences for OWL DL, and the URIs from the
>RDF(S) and
>> OWL vocabulary would then not be in any way special compared to any
>other URI.
>> In fact, there would not even exist URIs in the OWL vocabulary.
>>
>> An exception are probably a few URIs like 'owl:Thing' or
>'rdfs:comment', which
>> actually play a special role within the OWL 2 DL syntax. But then it
>would not
>> make sense to disallow /every/ URI from the RDFS and OWL namespace.
>Instead,
>> these few URIs could be treated specifically, or could be replaced by
>new
>> names.
>>
>> The only place where the disallowed vocabulary is really relevant is
>in the
>> reverse RDF mapping. There, it might happen in some situations that
>the
>> unrestricted usage of URIs from the RDF(S) or OWL vocabulary will lead
>to
>> confusion when one applies the mapping rules, be it by making a
>reverse
>> mapping impossible, or by leading to wrong results. This would then
>possibly
>> break the "semantic roundtripping contract", which states that
>roundtripping
>> from FS, through RDF and back to FS will always maintain the semantics
>of the
>> original OWL DL ontology.
>>
>> ! Proposal: Move the definition of the disallowed vocabulary from the
>DL
>> syntax document to the reverse RDF mapping.
>>
>> (C) Relaxation
>> --------------
>>
>> The argument in (B), that allowing certain RDF(S) or OWL vocabulary
>might lead
>> to technical problems with the reverse RDF mapping, cannot be used to
>disallow
>> /every/ URI from RDF(S) and OWL. Instead, it should really be checked
>for each
>> such URI whether it leads to problems with the reverse mapping or not.
>>
>> I had already some discussion on this topic for the concrete cases of
>rdf:List
>> [3] and RDF reification [4] (though the use of the latter wasn't
>disallowed in
>> OWL 1 DL, see (A)). And I think that in the analog way as discussed in
>these
>> mails, several other URIs could be made accessible in OWL 2 DL.
>>
>> One has to check this, of course, and this probably demands some
>effort. And
>> another question will be which of these URIs are of interest for
>custom usage
>> at all. However, as I have heard several times, there was a desire to
>make
>> more RDF graphs valid in OWL 2 DL. So here is a real chance to get
>more valid
>> OWL DL ontologies in RDF graph form!
>>
>> Best,
>> Michael
>>
>> [1] <http://www.w3.org/2007/OWL/wiki/Syntax#URIs_and_Namespaces>
>> [2] <http://www.w3.org/TR/owl-semantics/mapping.html#4.2>
>> [3] <http://lists.w3.org/Archives/Public/public-owl-
>wg/2008May/0188.html>
>> [4] <http://lists.w3.org/Archives/Public/public-owl-
>wg/2008May/0190.html>
>