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Re: RDF graph representation

From: Frank Manola <fmanola@acm.org>
Date: Fri, 23 Jul 2004 11:04:04 -0400
Message-ID: <410128E4.3010005@acm.org>
To: Jeremy Carroll <jjc@hplb.hpl.hp.com>
Cc: Dimitri Glazkov <dimitri.glazkov@gmail.com>, www-rdf-interest@w3.org

At the risk of referring to a topic lots of RDF folks would like to 
avoid (!), Figure 17 (illustrating reification) in the RDF Primer (see 
http://www.w3.org/TR/rdf-primer/#reification) uses exactly the technique 
Jeremy describes.  In the Figure, http://www.example.com/terms/weight 
labels both a node and an edge (the accompanying RDF/XML is in Example 19).

--Frank

Jeremy Carroll wrote:
> 
> Dimitri Glazkov wrote:
> 
>> This may be a bit of sophistry, but since predicate may be used as
>> subject (and object, I assume) in RDF, doesn't this make a
>> node-arc-node representation of a triple invalid?
>>
> 
> To play devil's advocate 'no'
> 
>> For instance, how would you represent an OWL property restriction in
>> such a graph mode? Wouldn't this mean that you'd have to point an arc
>> into the middle of another arc?
>>
>> Or am I missing something here? (which is probably the case)
>> Illuminate me please..
>>
> 
> Consider a graph
> 
> eg:a eg:b eg:c .
> eg:b eg:a eg:c .
> 
> OK so far?
> 
> So, the above representation *is* adequate since you are managing to 
> consider it.
> 
> We can draw the traditional diagram of this graph.
> It conveys the same information, and we can reconstitute the triples 
> from the picture. Thus, the representation is adequate.
> 
> Obviously, when trying to understand what it might mean, you have to 
> notice that the eg:b labelling one of the edges and the eg:b labelling a 
> node is the same. But that goes with many visual representations. e.g. 
> if you have an atlas, and the map of Eurasia is split over a number of 
> pages, with Berlin in two of them, you have to notice that this is the 
> same place because the two visual representations are labelled the same, 
> despite one being shown along with Paris, and the other being shown 
> along with Warsaw.
> 
> Visual representations *do* require the reader to do some work. The 
> traditional visual representation of the RDF graph, specifically 
> requires the user to notice when edge labels are the same (and when they 
> are the same as a node label).
> 
> Traditionally, edge labels are referred to as colours in graph theory. 
> The RDF graph is peculiar in having both coloured arcs and coloured 
> nodes (partially). But (the non-colour blind) would not see it as 
> strange being asked to notice that the blue edges were the same colour 
> as a blue node.
> 
> Jeremy
> 
> 
> 
> 
> 
> 
> 
Received on Friday, 23 July 2004 11:02:37 UTC

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