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>

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>

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 > peterReceived on Monday, 27 October 2014 23:19:11 UTC

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