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Re: RDF namespace URIs [was: FW: RE: Jena in Haystack]

From: Ralph R. Swick <swick@w3.org>
Date: Fri, 19 Jul 2002 08:39:51 -0400
Message-Id: <5.1.0.14.2.20020719082211.046a05d0@127.0.0.1>
To: "BASS,MICK (HP-USA,ex1)" <mick_bass@hp.com>, Dave Reynolds <der@hplb.hpl.hp.com>, karger@theory.lcs.mit.edu
Cc: www-rdf-dspace@w3.org, w3c-semweb-ad@w3.org

At 05:29 AM 7/19/2002 -0400, BASS,MICK (HP-USA,ex1) wrote:

>Forwarded to www-rdf-dspace for the record

Thanks, Mick.  I should send this reply to other fora, I suspect,
(like a public review comment on the RDF Core Working Drafts)
but I'll start with this one and add our Semantic Web
Advanced Development list.

>From: Dave Reynolds [mailto:der@hplb.hpl.hp.com]
>Sent: Monday, July 15, 2002 7:34 AM
>To: karger@theory.lcs.mit.edu
>Subject: Re: [dquan@mit.edu: jena evaluation]

...

>> 2. Predicates. For some odd reason, Jena mandates that predicate URIs
>> must contain at least one slash in them so that a namespace can be
>> deduced from it, ...
>...
>The issue is that according to the original M&S spec a predicate is
>identified
>by a QName (i.e. namespace plus local name part) but a predicate is also a
>specialization of a resource so it should have a URI of its own.

yes, sort-of

> The spec
>squares this circle by saying that the URI is the concatenation of the
>namespace
>and the localname part.

yes

> Now the problem is that if you only have the URI how

the predicate URI, I suppose you mean

>do
>you find the namespace/localname split? According to the RDF working group
>(though nothing is fixed until they survive Last Call) the algorithm is to
>work
>back from the right hand end of the URI until you find the first character
>which
>is not legal in an XML element production - for almost all RDF namespaces
>this
>is '#' because localnames are introduced using fragment-ids but in some
>cases
>can be '/' or other characters. 

I'll have to complain to the RDF Core WG then.   This
heuristic is unreliable and unnecessary.  You should
not have to deduce a namespace name at all; you
should be able to ask the Web explicitly.  If you _really_
need a namespace name and you don't have the Web
available to ask then you might want to resort to
heuristics such as these.

The RDF Schema proposal defines the property
http://www.w3.org/2000/01/rdf-schema#isDefinedBy
(see http://www.w3.org/TR/rdf-schema/#ch_isdefinedby )
for exactly this purpose.  You can ask the Web explicitly
by what namespace the property claims to be defined.

Well, too bad not many schemas remember to use
this property.  Even http://www.w3.org/2000/01/rdf-schema#
fails to use it itself.  sigh.

Let's encourage by example -- by writing code that uses
explicit references to namespaces with a property -- and
get the schemas to follow along.


>I'm curious as to what format predicate URIs you are using and whether they
>are
>legal RDF.

If jena believes that there is a URI that conforms to the URI RFC
but that is disallowed by RDF then we have a serious problem.
I'll have to pay closer attention to the RDF Core WG discussion
on this issue, I see.
Received on Friday, 19 July 2002 08:41:12 EDT

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