W3C home > Mailing lists > Public > www-rdf-interest@w3.org > January 2001

Re: Formation of RDF terms

From: Dave Beckett <dave.beckett@bristol.ac.uk>
Date: Fri, 26 Jan 2001 21:49:18 +0000
To: Aaron Swartz <aswartz@swartzfam.com>
cc: RDF Interest <www-rdf-interest@w3.org>
Message-ID: <25554.980545758@tatooine.ilrt.bris.ac.uk>
>>>Aaron Swartz said:
> Dave Beckett <dave.beckett@bristol.ac.uk> wrote:
> 
> > This is also useful when you have schemas that have no network
> > accessible URIs, very large schemas (e.g. Dewey for books) so you
> > don't want to use resolvable URIs for the namespace but might deliver
> > concepts in them and want to refer to the main schema -
> > [Classification XYZ in Dewey URI]->rdfs:isDefinedBy->[Dewey URI]
> 
> Is this a proper use of the isDefinedBy arc? I was under the impression that
> it should point to some sort of schema or spec that defined the URI. Would
> it be possible to use it to classify terms in groups like you're suggesting?

Well, I'm not an author of RDFS but in my opinion this is exactly the
situation that I would use it.  RDFS in s2.3.5 rdfs:isDefinedBy at
http://www.w3.org/TR/rdf-schema/#s2.3.5 says:

    The most common anticipated usage is to identify an RDF schema,
    given a name for one of the properties or classes defined by that
    schema. Although XML namespace declarations will typically
    provide the URI where RDF vocabulary resources are defined, there
    are cases where additional information is required.

The most common usage is to point to a schema - not required or only usage.

    For example, constructs such as
      <rdfs:subPropertyOf rdf:resource="http://purl.org/dc/elements/1.0/Creator"/>
    do not indicate the URI of the schema that includes the
    vocabulary item Creator (i.e., http://purl.org/dc/elements/1.0/).

This is the same kind of thing I was explaining with my Dewey
example.  Imagine that the Dewey RDF schema existed and it was 1GB in
size.  You wouldn't want to fetch it and find concept 'foo' inside it
as a fragment ID.  All you need is a small document describing the
concept 'foo' and a reference to Dewey so that your application can
recognise that.  The 'reference to Dewey' can be a URI with no
resolvable content or it could be the (RDF) schema.

In the above quote the example is the Dublin Core Metadata Element
Set schema (http://purl.org/dc/) and the Creator concept in that
schema and http://purl.org/dc/elements/1.0/Creator actually resolves
to a fragment of RDF inside an XHTML document - try it!

    In such cases, the rdfs:isDefinedBy property can be used to
    explicitly represent that information. This approach will also
    work when the URIs of the namespace and its components have no
    obvious relationship, as would be the case if they were
    identified using schemes such as GUIDs or MD-5 hashes.

... and this is exactly what we have been discussing.  This property
allows the relationship to be made without doing any delving into
parsing URIs - which isn't possible for general URIs.  I think RDF
shouldn't get into this game.

BTW I'm also going to the RDF-IG meeting in Cambridge

Dave
Institute for Learning and Research Technology (ILRT), http://www.ilrt.org/
Received on Friday, 26 January 2001 16:49:20 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Monday, 7 December 2009 10:51:47 GMT