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Re: Semantics and Abstract Syntax (and some general OWL Lite, CR, & implementation) comments

From: Bijan Parsia <bparsia@isr.umd.edu>
Date: Thu, 17 Jul 2003 11:59:43 -0400
Cc: public-webont-comments@w3.org
To: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>
Message-Id: <AE34E04C-B86F-11D7-8884-0003939E0B44@isr.umd.edu>

I'm satisfied by this response.

Bijan Parsia.

On Thursday, July 17, 2003, at 11:47  AM, Peter F. Patel-Schneider  

>> Subject: Re: Semantics and Abstract Syntax (and some general OWL  
>> Lite, CR, & implementation) comments
>> From: Bijan Parsia <bparsia@isr.umd.edu>
>> To: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>
>> Cc: public comments <public-webont-comments@w3.org>
>> Date: Thu, 19 Jun 2003 14:49:16 -0400
>> On Friday, May 30, 2003, at 03:41  PM, Peter F. Patel-Schneider wrote:
>>> This message responds to your comments, in each case not suggesting  
>>> any
>>> changes to the S&AS document.  This is not actually a rejection of  
>>> your
>>> comments, however.  I feel that you are generally satisfied with the
>>> situation as it stands, but that some improvements could be made, if
>>> possible.
>> Yeeess. I think that's right.
>>> One comment that you make corresponds to a re-opened issue that may
>>> result
>>> in a change - if this indeed happens we will let you know.
>> Qualified cardinalities right?
>> FWIW, I think this is a huge issue for many existing daml+oil users. I
>> worry that people will just try to use the daml vocabulary with OWL,
>> which seems icky.
> The Web Ontology working group reopened deliberations on qualified
> cardinality restrictions, but on 8 May 2003 decided to postpone work on
> qualified cardinality restrictions.  The official information on this
> postponement can be accessed at
> http://www.w3.org/2001/sw/WebOnt/webont-issues.html#I3.2-Qualified- 
> Restrictions
>>>> 1) Somewhat editorial: I think it would be invaluable for
>>>> implementors,
>>>> and even casual readers, to have the DLs that OWL Lite and OWL DL  
>>>> are
>>>> notational variants of (mostly) explicitly mentioned (they are,
>>>> respectively, to my best current knowledge, SHIF(D) and SHION(D)).
>>> Yes, the closest correspondences are to SHIF(D) and SHOIN(D), with  
>>> some
>>> limitations on how datatypes are treated.
>>> It would be useful to have this somewhere.  However, I don't think
>>> that the
>>> best place for this is in S&AS.
>> I strongly disagree. S&AS is, in my opinion, reasoner implementors  
>> will
>> go, especially those interested in implementing complete reasoners.
>> That was my experience, and I lost a LOT of time trying to figure out
>> how OWL lite was lighter than SHIF(D) (in a substantial way) and how
>> that made anything easier.
>> I would suggest that there be an "implementors note" break out box
>> somewhere early in S&AS, prolly toward the end of the Abstract Syntax
>> presentation. It could say something like:
>> *****
>> IMPLEMENTORS' NOTE: OWL Lite and OWL DL closely correspond to the
>> description logics known as SHIF(D) and SHION(D), with some limitation
>> on how datatypes are treated. The abstract syntax for  OWL Lite  
>> doesn't
>> contain many of the common explicit constructors associated with
>> SHIF(D), but the expressivity remains.
>> *****
>>> If you have a suggestion for a suitable
>>> place to stick this information, let us know.  (If the wording fits
>>> nicely
>>> in S&AS, it might even make it in there.)
>> I actually can't think of a better place to put it.
> This has been added as a Note just before Section 2.1.  To see the  
> change
> look in
> 	http://www-db.research.bell-labs.com/user/pfps/owl/semantics/
>> [snip]
>>>> I mean, given that OWL Lite can express general inclusion
>>>> axioms, what exactly does it help to have the restrictions on the  
>>>> left
>>>> hand sides of the various axioms? The syntactic restrictions seem to
>>>> only be of interest at the authoring or serialization level.
>>> The simpler axiom forms are intended to be reminiscent of frame
>>> systems.
>>> Most people write ontologies using mostly these forms, so it was
>>> decided to
>>> provide a syntax slanted towards them.  Some of this is already
>>> covered in
>>> Guide.
>> That explains why in the *concrete* syntax, but not in the *abstract*
>> syntax. I.e., why not
>> represent multiple subclassings as the subclass of an intersection (in
>> the abstract syntax)?
>> I mean, I could imagine that it would complicate the mapping to
>> triples, but I don't see off hand.
>> Are ANY users (as opposed to implementors) going to look at the
>> abstract syntax, or S&AS for that matter? If so, I would suggest that
>> S&AS should be made convenient for implementors, not end users. That
>> you have to use natural language to explain something that could  
>> easily
>> be directly expressed in the abstract syntax makes the abstract syntax
>> a bit less useful.
> This is a question that will most likely be answered by developers of
> OWL-related systems that include user interfaces.  It is probably  
> easier
> for implementors of such systems to internally use a syntax that is  
> close
> to syntax that they present to users, and the abstract syntax might be  
> such
> a syntax.
>>>> Similarly, even we have somewhat explicit intersections (from the
>>>> text), but nothing saying "intersectionOf" in the syntax. Ok, I
>>>> suspect
>>>> this makes the mapping to triples easier, but it makes understanding
>>>> the language from the implementation point of view much more
>>>> difficult.
>>> The tradeoffs in the syntax of OWL Lite are somewhat unusual.  The
>>> syntax
>>> of OWL Lite is supposed to be similar to frame syntax, thus the lack  
>>> of
>>> explicit intersectionOf.  I agree that from the logical point of view
>>> there
>>> is no reason for this, but it is supposed to be easier to write and  
>>> to
>>> parse.
>> Right, and that's fine for OWL lite, but it doesn't explain bubbling  
>> up
>> these restrictions to the Abstract syntax level.
> It is part of the design criteria of the abstract syntax to
> 	facilitate[] access to and evaluation of the language.  This
> 	particular syntax has a frame-like style, where a collection of
> 	information about a class or property is given in one large
> 	syntactic construct, instead of being divided into a number of
> 	atomic chunks ... [Section 2 of S&AS]
> which indicates that a more accessible syntax is better even though  
> that
> might somewhat obscure the actual expressive power of the language.
>>> There are short allusions to this in various places - a long allusion
>>> would be quite lengthy and probably not suitable.
>> I would accept language along the lines I gave above. My favored
>> solution would be a more explicit abstract syntax, but that's probably
>> too much work. But then there *really* needs to be a blocker of the
>> misunderstandings that in my own experience, and from that of my
>> students, are far too easy to make.
> The statement of correspondence between OWL Lite and SHIF(D) should  
> help
> here.
>> [snip]
>>>> ***************
>>>> 2) Completely Editorial: I would like the normative version of the
>>>> document to be a single HTML file. I know, off hand, of no other (at
>>>> least modern) W3C recommendation that is split up merely for
>>>> navigational purposes. It's inconvenient, it's inconsistent even  
>>>> with
>>>> the other OWL specs, and annoying, especially for offline reading.
>>> I agree somewhat, but do find the separated version to be helpful
>>> sometimes.  I was asked to make the switch from a single to a  
>>> compound
>>> document, and I'm not particularly interested in switching back.
>> Er...but none of the other documents, afaik, either in webont or
>> rdfcore are compound. Few if any, again afaik, modern W3C recs are
>> compound. I would have thought that that would be determinative :)
> OWL Test Cases is a compound document.
>> Not a biggy, but it does annoy me each and every time. And I often
>> forget that it's compound and thus load up only the first page and  
>> find
>> myself off line with not what I wanted. Oh well. Bookmarking the  
>> single
>> file will work. But I predict other people's annoyance.
>> [snip]
> No change is likely to be made here.
>>> Please respond, copying public-webont-comments@w3.org, as to whether
>>> you
>>> are satisfied with this response, whether you need to wait until
>>> certain
>>> changes to the design of OWL are done, or whether further
>>> correspondence is
>>> needed now.
>> CardinalityQ: need to wait
>> Adding "Implementors' note": I will be satisfied if something like  
>> this
>> is added. I won't be if not. I think
>> 	S&AS is exactly the right place for this information and it doesn't
>> seem like a large change.
> DONE, see above.
>> Single HTML file: Looking at: http://www.w3.org/2001/06/manual/#Large,
>> I'm not convinced that S&AS is actually "large" enough to count as a
>> large one. It certainly doesn't need compression to facilitate  
>> download
>> in most circumstances. But I guess if it is "large", then as long as  
>> the
>> other advice is followed, I can't strongly object. I might then object
>> that similarly long documents *aren't* broken up.
> NOT DONE, but as you say, it is possible to easily access the combined
> document.
>> Cheers,
>> Bijan Parsia.
> Please reply to public-webont-comments@w3.org as to whether you are
> satisfied.
> Thanks for your continuing comments.
> Peter F. Patel-Schneider
> Bell Labs Research
Received on Thursday, 17 July 2003 11:58:56 UTC

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