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Re: Punning discussion

From: Bijan Parsia <bparsia@cs.man.ac.uk>
Date: Thu, 24 Jan 2008 16:11:38 +0000
Message-Id: <AD5263FE-7ADC-4693-86D9-E1AEAA8D504E@cs.man.ac.uk>
Cc: "Web Ontology Language ((OWL)) Working Group WG" <public-owl-wg@w3.org>
To: "Michael Schneider" <schneid@fzi.de>

On 24 Jan 2008, at 14:41, Michael Schneider wrote:

> Bijan Parsia wrote:
>
>> On 24 Jan 2008, at 10:48, Michael Schneider wrote:
>> [snip]
>>>> From: Alan Ruttenberg
>>>> Sent: Tuesday, January 22, 2008 9:21 AM
>>>
>>>> 3) [...] How does punning effect OWL Full?
>>>
>>> Punning is a DL-only feature,
>>
>> This doesn't seem right. If you take the equality free fragment of
>> OWL Full, you cannot distinguish between punning and hilog semantics.
>> RDF, the language, doesn't have equality, so it is compatible with
>> punning.
>
> The aim is to provide an RDF compatible semantics, which has  
> additional
> semantics for all OWL-1.1 language features.

What this means is open to discussion.

> And the WG charter wants
> OWL-1.1-Full to maintain backwards compatibility with OWL-1.0-Full.

And would like to extend the compatibility, this might mean making  
slight changes to both. In either case, these are SHOULDs not MUSTs  
and it seems reasonable to see whether we can do better overall.
[snip]
> And to answer your statement above: There is, of course, an  
> 'owl:sameAs'
> construct both in the 1.1-RDF mapping, as in the 1.0-Full spec, and  
> it has a
> semantics in the latter. So I don't see how talking about "the  
> equality free
> fragment of OWL-Full" does help us in this discussion.

Well, you made a claim that somehow punning and OWL Full semantics  
were so radically different as to be incompatible. I pointed out a  
clear case where they coincide. I also, several times, have pointed  
out how the "mapping to one thing" style of RDF could be preserved  
and that, since RDF says nothing about equality, how we handle  
equality is more or less up to us.

>>> and cannot affect the definition of Full, as
>>> long as Full is understood to be an RDF compatible language.
>>
>> The semantics specs something in a style that is *suggestive* of how
>> to extend it to OWL, but that's a different thing. It doesn't say
>> *how* to extend the semantics. It seems as legitimate to add
>> parameterized extension relations as anything else.
>
> There is precedence given by the OWL-1.0-Full spec.

That's a *different* argument, i.e., it's not that OWL 1.0 Full is  
the only way to have an "RDF compatible model theory". You argued  
that we had no jurisdiction to change the RDF semantics. Let's say I  
agree. But then we *do* have jurisdiction to change OWL Full (as we  
are going to update it after all). Your argument against punning as  
the way we handle OWL Full is that its incompatible with RDF  
semantics. I've shown that's not true.

In this way I also have shown that punning is compatible with OWL  
Full with hilog semantics. (I.e., one can do the "One thing" mapping,  
have the parameterized IEXTs, then, in OWL Full, add an additional  
semantic condition to force extension merging).
[snip]
>> From the same paper I can see that it really seems to be possible  
>> to have
> real metamodelling

I don't find that hilog metamodelling to be more real than punning  
or, for that matter, less real that "true" second order logic or  
stratified approaches.

> (definition 6), at least in SHOIQ(D), without falling
> into undecidability.

You need to impose a unique name assumption on role names.

> But I haven't read the details yet, so you or Boris or
> anyone else may FIXME if I'm wrong. Nevertheless, it seems that it  
> has not
> been decided to use this "HiLog" semantics in 1.1-DL, for whatever  
> reason,
> but to use the weaker "contextual" (aka "punning") semantics instead.

There is no implementation experience (Boris and I have discussed  
some ideas but they could have a fairly large performance effect).  
It's pretty clearly not what people expect. Punning has a long  
history in Pellet so we have both user and implementor experience.  
It's also forward compatible as in you can add hilog semantics ontop  
of punning (as exhaustively discussed). So there's a pretty clear  
path forward if it turns out that people want and can use the hilog  
semantics.

> If you now lift your hand and honestly tell me that OWL-1.1-DL  
> allows this
> so called "HiLog semantics", too

What? Why would I say this? it's clearly false. And with excellent  
reason.

> (and, perhaps, that its left to the
> implementors of OWL-1.1 reasoners to decide which of these  
> semantics to
> support), then I promise to sit myself down and carefully check the
> technical details closely, and it may well be that I will never  
> stand up
> again and say a single evil word against "punning". :)

Sorry, I have never said, nor would I ever suggest, that punning  
includes hilog semantics. It's exactly as in boris's paper.

But that they are not the same doesn't make them incompatible. Given  
that there is no implementation of Hilog semantics, I conclude at  
this stage of the game that it's not used. It causes a number of  
problems and issues.

But if you want to include it in an OWL Full, fine. But you've  
already talked about giving up syntax reflection (in the precise  
style of OWL Full) so once you've gone there I think the burden of  
proof shifts a bit.

By the way, at just about every opportunity for over 3 years I've  
explained the difference between punning, hilog, and syntax  
reflection to as many users as I can. I spent on session discussing  
it at the first OWLED. I keep trying to get panels etc. etc. My  
experience is that the hilog (and syntax reflection), at least in  
full generality, is not anything people know about or when informed  
that they can see any use for. Or would be particularly good at  
working with. I worry a little about putting hilog into owl full  
(again) because when we *do* get a user base who understands and  
wants to use "implication heavy" metamodelling, there's no clear  
evidence that hilog (as opposed to stratified, for example) is what  
they'll want.

Standardization's primary goal, IMHO, is to support interoperability.  
I don't mind adding new features if we're likely to get multiple  
implementations (i.e., raise the floor), but this just doesn't seem  
to be the case here.

Cheers,
Bijan.
Received on Thursday, 24 January 2008 16:09:45 GMT

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