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Re: New Version of Networked Graphs Sail Available

From: Jeremy Carroll <jjc@hpl.hp.com>
Date: Thu, 18 Oct 2007 10:43:43 +0100
Message-ID: <47172ACF.6080903@hpl.hp.com>
To: Simon Schenk <sschenk@uni-koblenz.de>
CC: semantic-web <semantic-web@w3.org>, Sesame Developer discussion list <sesame-devel@lists.sourceforge.net>

Simon Schenk wrote:

> Networked Graphs are an extension of named graphs, which allow to define
> a graph both extensionally by listing triples (as in named graphs), but
> also intensionally through views. Views are expressed using SPARQL
> queries and are included into graphs using a simple RDF syntax. To
> express that some graph G should contain the results of a query Q, we
> simply add a statement (G ng:definedBy Q^^ng:Query) to G. Views can use
> negation as failure, just as normal SPARQL queries and can recursively
> depend on each other. The reasoning engine will resolve this recursion.
> A graph can at the same time contain intensionally and extensionally
> defined statements. 

This seems overly complicated.

The named graphs framework is meant to be a very simple extension to RDF.

In my opinion, a view such as (G ng:definedBy Q^^ng:Query) should either 
be obviously true or obviously false for some interpretation. The 
simplest way is that Q is a query that returns a graph, and either I(G) 
is isomorphic to this graph, (in which case the statement is true in the 
interpretation I) or it isn't in which case the interpretation is false.

There is an issue to do with loops in the definitions - I would have 
thought that the simplest approach is to (weakly) prohibit them. i.e. 
every definition is required to be grounded, where:

a) if we know that URI u names graph g, then u is grounded
b) if we have a URI u that names a graph via query Q that depends on 
graphs named u1, u2, ... uk and each of u1, u2, ... uk is grounded then
u is grounded.


> A detailed specification of Networked graphs can be found in [3].
> [3] http://www.uni-koblenz.de/~sschenk/publications/2007/ngtr.pdf

I'll read this and get back if it convinces me that my above post is 
Received on Thursday, 18 October 2007 09:44:15 UTC

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