# Re: RDF Graphs

From: Peter F. Patel-Schneider <pfpschneider@gmail.com>
Date: Mon, 27 Oct 2014 16:18:40 -0700
Message-ID: <544ED2D0.20205@gmail.com>
To: Hugh Glaser <hugh@glasers.org>
CC: Melvin Carvalho <melvincarvalho@gmail.com>, Pat Hayes <phayes@ihmc.us>, Semantic Web <semantic-web@w3.org>
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On 10/27/2014 04:04 PM, Hugh Glaser wrote:
> Thanks Peter, that’s so helpful and succinct I can get rid of the history!
>
>> On 27 Oct 2014, at 22:52, Peter F. Patel-Schneider <pfpschneider@gmail.com> wrote:
>>
>> I don't see why you should worry about an RDF graph not being exactly a simple graph.  There are lots of situations where modifiers are not subsective.
> There are two reasons in Maths to use a term, I think.
> One of them is to appeal to some pre-defined idea of the structure of things, so that the structure under discussion can be communicated quickly.
> The other is to then appeal to a pre-existing body go knowledge about such structures.
>
>> For example, a directed graph is not exactly a graph.
> True, but all directed graphs are graphs;

Not so.  If you take a directed graph and ignore the direction you get a
multigraph, not a graph.  Further some important graph terms, including
connectivity, have to be redefined for directed graphs, they don't just follow
from the underlying terms on undirected graphs.

> so using the term “graph in “directed graph” is helpful - it conveys structure by referring to previously understood things, and also allows me to lean on other Graph Theory results.
>> What counts is that an RDF graph can be considered to like a sort of a graph, and it is.
> Ah, so what “sort of graph”?
>>
>> The normal definition of a graph is a pair consisting of a set of nodes and a set of edges, so there is no problem with saying that an RDF graph is defined as a set of triples.
> Only if you can establish the correspondence between a set of triples and a graph.
>>
>> Mathematics is full of cases where new notions are defined by modifying or extending old ones.
> Yes, but usually only when helpful, as above.
>
> Does it help to communicate what RDF looks like?
> Well sometimes, but it also misleads, as I said.
> Can it use existing results from Graph Theory? - well (I think?) only if it has certain, characteristics, which I think are actually quite unsual.

>> peter
> Cheers
> Hugh
>

peter
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Received on Monday, 27 October 2014 23:19:11 UTC

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