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Re: For namespace reuse

From: Ivan Herman <ivan@w3.org>
Date: Tue, 03 Jun 2008 10:34:44 +0200
Message-ID: <48450224.4080702@w3.org>
To: Bijan Parsia <bparsia@cs.man.ac.uk>
CC: OWL Working Group WG <public-owl-wg@w3.org>
Bijan,

although I fully understand and agree with the frustration on the 
namespaces that no one remembers (me neither), I am afraid we might have 
to separate the OWL/XML namespace from the OWL one (I think we did agree 
that we would reuse the same OWL namespace for OWL2, so the issue is 
really only between these two).

Caveat: I am not a real XML expert, and we might want to ask advise from 
one if we continue to disagree:-). While I give some of my thoughts 
below why I think those two should be separated, I must admit that I 
also have a general feeling that "something else might go wrong that I 
do not know about, let us avoid possible problems for the future". I 
know this is not a rational argument but, well...:-)

First of all: you say "http://www.w3.org/2002/07/owl#", which is the 
right namespace for OWL, but probably not in the 'real' XML sense which 
should be "http://www.w3.org/2002/07/owl" (note the missing '#'). So 
there you go: there is already a difference:-(

One of my problems is that, conceptually, the usage of namespaces in the 
RDF world is very different from the XML world (yes, I know, RDF/XML 
uses the namespaces, and I am not sure it is 100% kosher in the XML 
sense...). In the case of RDF, namespaces are really used for an 
abbreviation of URI-s, much as CURIE-s do (and will be used in the 
functional syntax). Hence the usage of the '#' or '/' characters in the 
URI-s we use. In the XML world, namespaces have an effect on the 
abstract 'meaning' of the XML (I use the word _very_ loosely here!): 
they are indeed integral part of the XML Infoset, affect the way the DOM 
works, etc. Hence also their usage of URI-s without the fragment part, 
ie, the '#' character (as far as I know, formally, the meaning of '#' 
and what comes after it, is dependent on the mime-type, it does not have 
a generic meaning, that is why the XML community keeps away using it there.)

Another point: in the RDF world, a possible action is to dereference the 
URI in the namespace and hope to see, eg, the RDF/XML representation for 
the terms. I know this is does not always work (eg, for the XSD 
namespace) but it certainly works for

http://www.w3.org/2002/07/owl#

or

http://www.w3.org/2002/07/owl

already! (And I would not expect us to change the existing file there by 
removing anything and hence creating backward compatibility problems, 
just adding the new OWL 2 terms, eventually.) I do believe this becomes 
more an more common with people using RDF, eg, using the various RDF 
browsers (tabulator, zeitgeist, disco, etc) and I believe it is a strong 
requirement for communities like the Linking Open Data one, for example, 
have in their practice (we can check this for more specific references 
if we want). As a purely anecdotal fact, I know that when I mix 
different vocabularies and I am not sure about the exact term, my first 
instinct is to try to dereference the URI and see what is there. I do 
that fairly often. Sure, when I have a bookmark against the textual 
specification of the terms I use that (say, for DC or indeed OWL), but 
that is not always the case.

However, if you look at the same URI from an XML sense, you would expect 
something different. The dereferenced URI would give information on the 
terms used in the XML space ie, in our case, Declaration, 
ObjectAllValuesFrom, etc. These are not RDF terms (I would not use 
owl:ObjectAllValuesFrom in RDF), they are specific to the OWL/XML only. 
Ie, I would not want to see these terms listed there as an RDF user, 
because it would just mess me up... Whether what you have at the end of 
that URI is in RDDL format or anything else (and I agree RDDL is a good 
idea) is a secondary issue.

B.t.w., we did discuss some possible URI-s for RDF/XML at the telco, but 
we did not consider:

http://www.w3.org/2002/07/owl/xml

which might certainly ease the pain, being a logical step from the core 
OWL namespace...

Cheers

Ivan


Bijan Parsia wrote:
> 
> Hiya,
> 
> Sorry I missed last week. I'd like to put in a plea for reusing:
>     http://www.w3.org/2002/07/owl#
> everywhere possible, including the OWL/XML serialization format.
> 
> As it stands, we often have way too many namespaces just to get off the 
> ground (rdf, rdfs, owl, and xsd!). (I can't remember *any* of them.) 
> Given that there will be absolutely no confusing qnames of elements and 
> uris of properties and classes, I think we should default to minimizing 
> extra syntactic noise.
> 
> At the very least, I think we need a very strong argument or set of 
> arguments, preferably grounded in reasonable common behavior.
> 
> I saw from the minutes that some people suggested that people will click 
> on the namespace. First, I don't think that's particularly common, 
> anywhere. Second, I have no problem putting up RDDL document at the OWL 
> namespace (indeed, that's where it should be). So I don't see that case 
> is worth the tax of Yet Another OWL URI. Even if people do do it, it's 
> typically seldom. Whereas managing several uris in headers is far more 
> common (or if it isn't, then something has gone very wrong!)
> 
> Cheers,
> Bijan.
> 

-- 

Ivan Herman, W3C Semantic Web Activity Lead
Home: http://www.w3.org/People/Ivan/
PGP Key: http://www.ivan-herman.net/pgpkey.html
FOAF: http://www.ivan-herman.net/foaf.rdf


Received on Tuesday, 3 June 2008 08:35:11 GMT

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