Re: OWL and RDFS (from public-webont-comments@w3.org)

At 16:02 +0200 4/6/03, Davide Noaro wrote:
Message-ID: <001301c2f9c8$08be7470$221f0125@shadow>
From: "Davide Noaro" 
<<mailto:noarodavide@libero.it?Subject=Re:%20[closed]%20Re:%20OWL%20Questions!&amp;In-Reply-To=&lt;001301c2f9c8$08be7470$221f0125@shadow&gt;&amp;References=&lt;001301c2f9c8$08be7470$221f0125@shadow&gt;>noarodavide@libero.it>
To: 
<<mailto:public-webont-comments@w3.org?Subject=Re:%20[closed]%20Re:%20OWL%20Questions!&amp;In-Reply-To=&lt;001301c2f9c8$08be7470$221f0125@shadow&gt;&amp;References=&lt;001301c2f9c8$08be7470$221f0125@shadow&gt;>public-webont-comments@w3.org>
Date: Thu, 3 Apr 2003 12:01:45 +0200
Subject: Re: [closed] Re: OWL Questions!

Thank you very much for your answers,
but i don't understand well.....

you say:

>1 - OWL is an extension of RDF(S) -- that is, all RDF and RDFS
>documents are legal OWL Full documents 

OK!! If OWL is an extension....

>and all OWL documents are
>legal RDFS documents

I should have been clearer -- the issue is one of what we mean by 
being legal documents,  currently all RDF documents are legal RDFS 
documents and all RDFS documents are legal RDF documents - but RDFS 
is more expressive than RDF, right?  THe reason is that an RDF 
document using no RDFS terms is still parsable by RDFS tools, they 
can build the right graph, there's just no additional "semantics" 
from the RDFS space.  RDFS documents don't break RDF parsers, but an 
"RDF tool" won't understand "rdfs:class" as anything other than any 
other term.   There
are many ways to describe this relation -- I'll use the term 
"vocabulary extension" to mean there are some additional terms in 
RDFS that add new "meaning" to RDF but use the same syntax.


HOW is it possible if OWL allow more expressivity than RDFS??
So OWL and RDFS are equivalent ....

so OWL FULL is to RDFS as RDFS is to RDF -- that is OWL Full is a 
"vocabulary extension" to RDFS.


and after you say:

>Not all RDFS documents are necesssarily in OWL Lite or OWL
>Full.

this should have said OWL LITE or OWL DL.  These sublanguages have 
some specific restrictions.  But all RDFS documents are necessarily 
in OWL Full (essentially I mean that an OWL Full tool would be 
expected to correctly handle all RDFS)


So not ALL RDFS documents are OWL documents i understand....

but that is wrong, they are OWL documents, but not necessarily OWL 
Lite or OWL DL documents


Have you make a mistake in writing or is all true what have you said?

the mistake was on my part - as I explained above

************************************************************************************
Here what i have understand:

- OWL is an extension of RDFS and allow more expressivity than RDFS, 
in fact you can, for example say that a
property is required (owl:minCardinality of 1) or optional
(owl:minCardinality of 0) and other such things than IN RDFS YOU CAN'T!

well, you can, but it won't have any special meaning.  That is, to an 
RDFS tool, owl: is just an arbitrary namespace and thus it will build 
the correct triples, but not interpret them to mean required and 
optional and the like.



-SO RDFS document are valid OWL documents, but NOT ALL OWL documents 
ARE  VALID RDFS DOCUMENTS.
( e.g. owl document in which i use owl:minCardinality, that in rdfs 
doesn't exist )

again, it does exist, but it doesn't take on the specialized meaning


********************************************************************************************

Thanks if you can clarify me again the situation.
Davide.

I realize the above remains confusing, but it is usually the case 
when we add semantically relevant vocabulary to an extensible 
language -- the analogy "RDFS is to RDF as OWL Full is to RDFS" 
holds.  For OWL Lite and DL it doesn't hold, but it is important to 
understand where it does and doesn't hold, which is why the Web 
Ontology group put so much time and effort into documenting this and 
working out the details



       -----------------------------------------------------------
       Davide Noaro
       
<mailto:noarodavide@libero.it?Subject=Re:%20[closed]%20Re:%20OWL%20Questions!&amp;In-Reply-To=&lt;001301c2f9c8$08be7470$221f0125@shadow&gt;&amp;References=&lt;001301c2f9c8$08be7470$221f0125@shadow&gt;>noarodavide@libero.it
       ------------------------------------------------------------ 


-- 
Professor James Hendler				  hendler@cs.umd.edu
Director, Semantic Web and Agent Technologies	  301-405-2696
Maryland Information and Network Dynamics Lab.	  301-405-6707 (Fax)
Univ of Maryland, College Park, MD 20742	  240-731-3822 (Cell)
http://www.cs.umd.edu/users/hendler

Received on Sunday, 6 April 2003 12:57:49 UTC