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Re: RDF Graphs

From: Antoine Zimmermann <antoine.zimmermann@emse.fr>
Date: Mon, 27 Oct 2014 16:44:13 +0100
Message-ID: <544E684D.4010904@emse.fr>
To: semantic-web@w3.org
The abstract of RDF 1.1 Concepts and Abstract Syntax says:

"RDF graphs are sets of subject-predicate-object triples, where the 
elements may be IRIs, blank nodes, or datatyped literals."

http://www.w3.org/TR/rdf11-concepts/#abstract

The more formal definition is given in Section 3:

"An RDF graph is a set of RDF triples."

and:

"""
An RDF triple consists of three components:
  - the subject, which is an IRI or a blank node
  - the predicate, which is an IRI
  - the object, which is an IRI, a literal or a blank node
"""

http://www.w3.org/TR/rdf11-concepts/#dfn-rdf-graph


So, in fact, an RDF Graph is not a graph (in the usual mathematical 
sense), but it can be mapped to a directed (edge-and-node-)labelled 
multigraph.

In your exemple, G is the singleton {(rdfs:label,rdfs:label,"Label")}.


--AZ.



Le 27/10/2014 16:26, Hugh Glaser a écrit :
> Everyone talks about RDF Graphs, and I have sort of puzzled over what an RDF Graph is - so I thought I would ask.
>
> Sorry if you just need to point me at some W3C resource somewhere.
>
> "This linking structure forms a directed, labeled graph, where the edges represent the named link between two resources, represented by the graph nodes. This graph view is the easiest possible mental model for RDF and is often used in easy-to-understand visual explanations.”
> (http://www.w3.org/RDF/ )
> (I strongly agree with the second sentence, by the way!)
>
> Simple Graphs are usually G = (V, E) comprising a set V of vertices together with a set E of edges, but that doesn’t seem to describe RDF Graphs for me.
>
> The sort of thing that I am considering is an RDF Graph such as:
>
> rdfs:label rdfs:label “Label” .
>
> Is it G = ({rdfs:label, “Label”}, {(rdfs:label, “Label”)} with edge-labelling function (rdfs:label, “Label”) => rdfs:label ?
> So we need to have both a vertex and an edge label with value rdfs:label, and they don’t really have a logical connection.
> Sort of worrying?
>
> Is that the sort of graph an RDF Graph is, and is that how it is formally defined?
>
> Also, a "labeled graph” usually refers to the vertices being labelled; should it not say that RDF is a “directed, edge-labelled graph”?
>
> Not exactly my forte this, so I am hoping I will be able to understand any answers!
> Best
> Hugh
>

-- 
Antoine Zimmermann
ISCOD - Institut Henri Fayol
École des Mines de Saint-Étienne
158 cours Fauriel
CS 62362
42023 Saint-Étienne Cedex 2
France
Tél:+33(0)4 77 42 66 03
Fax:+33(0)4 77 42 66 66
http://zimmer.aprilfoolsreview.com/
Received on Monday, 27 October 2014 15:43:54 UTC

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