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Re: Questions about RDF

From: Dan Brickley <Daniel.Brickley@bristol.ac.uk>
Date: Tue, 3 Jul 2001 08:49:31 +0100 (BST)
To: Kshemendra Chaturvedi <kshemendra.chaturvedi@ascom.com>
cc: www-rdf-interest@w3.org
Message-ID: <Pine.GSO.4.21.0107030834350.12625-100000@mail.ilrt.bris.ac.uk>

Hi

On Tue, 3 Jul 2001, Kshemendra Chaturvedi wrote:

> Hi All,
> I have a few queries about RDF, which are like these:
> 
> - In the RDF schema the properties belonging to a particular domain
> (class), do they form an
> ordered sequence. In other words, in the RDF data model, the properties of
> the resource have to
> be in the same sequence the way they are in RDF schema.

No; they are unordered. RDF provides some utility vocabulary (the
container constructs rdf:Bag, rdf:Seq and rdf:Alt) to support
representation of orderings. Other techniques can be used instead. I
think DAML+OIL (see http://www.daml.org/) provides a different mechanism
for containers.

> - Is it possible to specify the default value of the property.

No, not in using the core RDF specs.

> 
> - Is it possible to define a property as unique.

Again, no, not using the core RDF specs. However DAML+OIL provides a way
to represent unique and unambiguous properties.

> 
> - Does RDF support an open content model like many other schema languages
> (e.g. XDR)

In a sense, yes, although the notion of 'open content model' isn't
directly applicable to RDF, since it is associated with the
containment-oriented data model of the XML Infoset. RDF generally has a
rather 'open' attitude to the kind of content you can model in an
RDF/XML document... The RDF design in general allows new information to
be added in alongside old. In other words, the content of an XML/RDF
document can contain all sorts of assertions, and the kind and number of
assertions you make are not heavily restricted by the RDF schemas for
the namespaces you're using. By contrast, XML schema languages tend to
focus on restricting the exact contents of XML documents. The W3C "Web 
Data" Note, describes this contrast a bit more carefully than I
have. See http://www.w3.org/1999/04/WebData for detail.

Hope this helps,

Dan


> 
> 
> Thanks
> Kshemendra
> 
> 
Received on Tuesday, 3 July 2001 03:50:59 GMT

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