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New Version of Networked Graphs Sail Available

From: Simon Schenk <sschenk@uni-koblenz.de>
Date: Wed, 17 Oct 2007 17:19:00 +0200
To: semantic-web <semantic-web@w3.org>, Sesame Developer discussion list <sesame-devel@lists.sourceforge.net>
Message-Id: <1192634340.7196.31.camel@lapace01>
Dear all,

I am happy to announce version 0.3 of the Networked Graphs Sail for the
Sesame2 RDF repository [1], which is available for download at [2].

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. 

A detailed specification of Networked graphs can be found in [3].

By popular demand this version has a several interesting new features:

      * Works with Sesame 2.0 beta 6 without any additional patches (The
        formerly needed patches for dataset support have been integrated
        into standard Sesame).
      * Supports default dataset (no need for FROM clauses in views any
        more.) Handle with care - this can be resource intensive, as it
        creates views on your whole repository.
      * Supports views in the null context. Simply use ng:NullContext as
        subject of your view definitions.
      * Does not forbid blank node creation in CONSTRUCT patterns any
	more. Handle with care - this can lead to infinite models and
	hence to infinite recursion in the reasoning engine.
      * Fixes all known bugs as of 2007-10-17

A Sesame repository for testing purposes is available at [4]. [4] is a
SPARQL and Sesame HTTP endpoint. It can be queried using any SPARQL
aware tool. You can query, add and modify data using a Sesame2
HttpRepository or the openrdf-workbench, which you can access at [5].
The repository contains some test data [6]. You will get the idea of
networked graphs by executing queries like 
"SELECT * FROM <http://ex.org/graph2> WHERE {?s ?p ?o}"
with and without including inferred statements. In case anything gets
broken, simply clear the repository and re-upload the data from [6].

While with this endpoint you still need to collect all neccessary
graphs before evaluating views, future versions will allow to
transparently forward (sub-)queries to remote SPARQL endpoints. 

Best regards,

[1] http://www.openrdf.org
[2] http://isweb.uni-koblenz.de/Research/NetworkedGraphs
[3] http://www.uni-koblenz.de/~sschenk/publications/2007/ngtr.pdf
[5] http://k-sems.uni-koblenz.de:8180/openrdf-workbench
[6] http://www.uni-koblenz.de/~sschenk/software/NGTestGraphs.trig

Simon Schenk | ISWeb | Uni Koblenz-Landau

Received on Wednesday, 17 October 2007 15:19:13 UTC

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