Re: LC responses 28, 48 & 58

Peter F. Patel-Schneider wrote:
> From: Ivan Herman <ivan@w3.org>
> Subject: Re: LC responses 28, 48 & 58
> Date: Wed, 11 Mar 2009 17:45:15 +0100
> 
[skip]

> 
>> On my way back home from the 'tute I tried to combine some sort of an
>> "ideal" (a.k.a. more mathematical) view of the various components and
>> their naming with the accepted practice as referred to by Jim and
>> Michael (and Frank, actually). Here is what I think we have
>>
>> - We have OWL 2 (no suffix!). This is defined in the structural spec,
>> essentially via UML. It has a representation in RDF using the OWL 2
>> vocabulary. RDF graphs that 'behave' well v.a.v. data types (this is my
>> understanding from Boris) can be mapped to the UML. In other words,
>> modulo some misbehaving RDF graphs (that are rare in practice) the UML
>> structure and the RDF are equivalent.
> 
> Close.  RDF graphs that violate some of the conditions in SS&FS cannot
> be nicely or uniquely mapped back to the SS.
>

Boris will have a more precise set of restrictions we can refer to.


>> - We have two possible semantics for OWL 2: Direct and RDF Based. Both
>> can be used with all RDF graphs.
> 
> Not quite.  The direct semantics cannot handle RDF graphs that misuse
> literals or facets.  (That is, the direct semantics doesn't say what to
> do with "abd"^^xsd:integer.)  
> 

Oops, you are right. But isn't that covered by those RDF graphs that can
be mapped back on SS?

>> - We also have syntactic subsets of OWL 2. These are the OWL DL
>> Syntactic Subset, and the OWL EL/QL/RL syntactic subsets. We can also
>> consider OWL 2 as a whole as a syntactic subset with empty restrictions.
> 
> These are OWL 2 DL and OWL 2 EL/QL/RL.
> 

Well, that is the point, I guess. The profile document talks
_exclusively_ about syntactic subsets. It does not talk about which of
the two semantics is used for a specific subset. Isn't it perfectly
feasible that tomorrow somebody comes and makes an nice implementation
of the OWL QL _syntactic_ subset based on the RDF Semantic? What would
that be called then?

That is why, at least in my mind, a syntactic subset of OWL 2 and its
adopted semantics are separate things. We have to live with the current
understanding out there (as Michael, Jim, and Frank all said), so the
term 'OWL DL' and 'OWL Full' are indeed used as syntactic subsets + a
specific semantics, hence the issue we have with the naming...


>> - The combination of any subsets with any of the two semantics are
>> possible. 
> 
> These subsets behave nicely, yes.
> 
>> However, only certain combinations have proven to be useful in
>> practice for different reasons. These are:
>>
>>  - The whole of OWL 2 using the RDF Based Semantics; this is commonly
>> referred to as OWL 2 Full. Note that OWL 2 Full has the extra bonus of
>> providing semantics for those [unusual] RDF graphs that cannot be mapped onto
>> the OWL 2 Structure.
> 
> OK.
> 
>>  - The OWL DL Syntactic Subset and the Direct Semantics, this is
>> commonly referred to as OWL 2 DL
> 
> OWL 2 DL is often overloaded to mean the combination of OWL 2 DL
> ontologies under the direct semantics.
>

Yes. If we started from fresh, my approach would be to refer to OWL 2 DL
exclusively as the syntax (ie, the syntactic subset) _without_ the
attached semantics. But, since 2004, the general public has used this
term as a combination, and we have to honour that.

>>  - The OWL EL and QL Syntactic Subsets and the Direct Semantics, these
>> are commonly referred to as OWL EL and OWL QL
> 
> Ditto.
> 
>>  - The OWL RL Syntactic Subset and the RDF Based Semantics, this is
>> commonly referred to as OWL RL. Note that a separate theorem shows that,
>> in many important cases, the OWL RL Syntactic Subset can actually be
>> used with both Semantics and they behave in an identical manner, ie,
>> both combinations are meaningful.
> 
> Maybe.
> 
>> In other words, we may want to strictly separate the notion of _OWL XX
>> Syntactic Subset_ and certain combination of these with particular
>> semantics.
> 
> Yes, but we also want to do this in a way that doesn't say SS so much.
>

'SS' = structural syntax or 'SS' = syntactic subset ?

>> Is this what Michael refers to? Can that be put into a better language
>> (maybe we will have to find a better name for OWL XX Syntactic Subset)
> 
> OWL 2 XX works for me.
>

See above why I am not sure it is right...

Cheers

Ivan




>> I am not sure it helps; it helped to clarify my thoughts on the bus...
>>
>> Ivan
> 
> peter

-- 

Ivan Herman, W3C Semantic Web Activity Lead
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