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Re: RDF Question: about syntax of rdf container objects (Bag, Alt, Seq)

From: Dan Brickley <Daniel.Brickley@Bristol.ac.uk>
Date: Thu, 8 Apr 1999 11:46:11 +0100 (BST)
To: "'xml-dev@ic.ac.uk'" <xml-dev@ic.ac.uk>
cc: www-rdf-comments@w3.org
Message-ID: <Pine.GHP.4.02A.9904081136540.5270-100000@mail.ilrt.bris.ac.uk>

(cc'd to www-rdf-comments; please trim from any followups on xml-dev)

On Thu, 8 Apr 1999, Roger L. Costello wrote:

> In section 3 of the RDF Model & Syntax spec it talks about containers,
> e.g., rdf:Bag, rdf:Alt, and rdf:Seq.  It gives an example where the
> model and syntax is shown for the following statement:
> 
> "The students in course 6.001 are Amy, Tim, John, Mary, and Sue."
> 
> The model for this statement shows a resource, /courses/6.001, having a
> property, students, whose value is an anonymous resource (i.e., a
> resource with no identifier).  The anonymous resource has an rdf:type
> property  whose value is rdf:Bag.  It has a property rdf:_1 whose value
> is /Students/Amy.  It has a property rdf:_2 whose value is
> /Students/Tim, etc.
> 
> The spec shows the syntax for this model as:
> 
> <rdf:RDF>
>     <rdf:Description about="http://mycollege.edu/courses/6.001">
>       <s:students>
>         <rdf:Bag>
>           <rdf:li resource="http://mycollege.edu/students/Amy"/>
>           <rdf:li resource="http://mycollege.edu/students/Tim"/>
>           <rdf:li resource="http://mycollege.edu/students/John"/>
>           <rdf:li resource="http://mycollege.edu/students/Mary"/>
>           <rdf:li resource="http://mycollege.edu/students/Sue"/>
>         </rdf:Bag>
>       </s:students>
~>     </rdf:Description>
>   </rdf:RDF>
> 
> This confuses me.  It does not seem to faithfully represent the model.  
> Recall that the model says that resource, /courses/6.001, has a
> property, students, whose value is an *anonymous resource*.  This syntax
> does not seem to be expressing that.  This syntax says that the value is
> an rdf:Bag, not an anonymous resource. [...]

The value is *both* an rdf:Bag and an anonymous resource. Just because
we don't have an identifier for the resource, it doesn't mean we can't know
other properties of it (such as its type, ie. the class of which it is a
member). The syntax tells us that it is a Bag, but doesn't give a URI or
ID to represent that Bag.

Having an rdf:type property pointing to rdf:Bag is just RDF's way of
telling us that the anonymous resource "is A" rdf:Bag. I suspect "type"
rather than "isA" was used to name this relation/property since "isA"
is sometimes used ambiguously, ie. also used as a name for the
"subClassOf" relation.

Hope this helps,

Dan




--
Daniel.Brickley@bristol.ac.uk                  
Institute for Learning and Research Technology http://www.ilrt.bris.ac.uk/
University of Bristol,  Bristol BS8 1TN, UK.   phone:+44(0)117-9287096
Received on Thursday, 8 April 1999 06:46:20 GMT

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