Re: Suggestion to change RDF encoding of HasKey axioms [RE: I've implemented the change to the syntax of HasKey]

Michael,



Michael Schneider wrote:
>> -----Original Message-----
>> From: Ivan Herman [mailto:ivan@w3.org]
>> Sent: Saturday, March 21, 2009 7:41 AM
>> To: Michael Schneider
>> Cc: W3C OWL Working Group; Boris Motik
>> Subject: Re: Suggestion to change RDF encoding of HasKey axioms [RE:
>> I've implemented the change to the syntax of HasKey]
>>
>> If I put an RDF+RDF base semantics user's hat on, isn't it correct that
>> the same property may be used both as an object and a data property? 
> 
> Yes.
> 
> (And if we /would/ allow for object/data property punning in DL,
> the situation would be similar there, too.)
>

Apage satanas! Do not even think of reopening that issue:-)

I do not think there is anything below that we would really disagree
about... I am just looking what the most 'natural' way for RDF users to
use Keys (which I find damn useful and I expect it will be widely used!)

So, just as a thought experiment: why not say that, by default,
properties listed in a hasKey are object properties (ie, I can put there
a list of properties, simply), but I can have a separate list which
explicitly lists datatype properties? Ie,

- if I want to have FS-compatible encoding, I would separate these two
and make the encoding proper in FS
- if I do not really care about FS, I would probably disregard the
datatype property part of keys and just use the list of properties.

Ivan

>> Ie,
>> in many cases I would not really really care about this distinction. 
> 
> You may always put every property in the owl:keyObjectProperties list 
> and leave the data property list empty.
> 
>> For
>> such cases isn't it correct that the separation of the key properties
>> would look fairly artificial?
> 
> If you do not want the fine grained distinction, then maybe. 
> But equally well it could be asked
> 
> * why the additional class?
> * why more than one property?
> * Why keys at all, we have IFDPs in Full?
> 
> Key axioms are pretty flexible beasts which give authors a lot of control
> over how they want to define keys. And in Full, as much as possible of this
> flexibility should be reflected in the RDF-Based Semantics.
> 
> I wouldn't call Keys a "typical" OWL Full language feature. (They are
> special enough, that they deserve their own semantic condition table. :-))
> But they are in OWL 2 now, so their intended semantics should be supported
> as precisely as possible. Doing so, that's the job of the one with the 
> RDF Based Semantics Editor's hat on. :-)
> 
> With the data property list, the included properties can then be
> entailed to be data properties, without saying so. Currently,
> the semantics only say that all the properties involved are, well,
> properties.
> If a property is intended to be a data property, this information has to
> come from a different source (e.g. from an explicit declaration triple).
> 
> In your other mail:
> 
>> Sorry to have forgotten to add this to my previous mail. Again in OWL 
>> Full I could also use annotation properties in a key, right? 
> 
> Yes, you can put everything you want into a key axiom (even cats and dogs,
> as Peter likes to say :)). But a key axiom will simply ignore that 
> something is (also) an annotation property. It will, however, infer
> that something is (also) a data property, if you put it in the
> data property list. And this additional information may or may not
> be a win for reasoners or other processing tools, or simply for people
> working with the ontology.
> 
>> Of course, 
>> annotation properties are just (object) properties in owl full, but the 
>> explicit requirement in the key axiom would still be a bit disturbing 
>> for owl full users...
>>
>> Ivan 
> 
> Keys are for those who need/desire them. No OWL Full user is forced to 
> use key axioms in his ontology. But if an OWL Full user uses them,
> and provided that he knows well what they are for, then I do not see
> a reason to bother about the explicit distinction between data and
> object properties.
> 
> Cheers,
> Michael
> 
> --
> Dipl.-Inform. Michael Schneider
> Research Scientist, Dept. Information Process Engineering (IPE)
> Tel  : +49-721-9654-726
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-- 

Ivan Herman, W3C Semantic Web Activity Lead
Home: http://www.w3.org/People/Ivan/
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