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Re: resources for network-based/hierarchical RDF store

From: Andreas Langegger <andreas.langegger@gmx.at>
Date: Fri, 27 Apr 2007 16:22:50 +0200
Message-ID: <4632073A.8030700@gmx.at>
CC: semantic-web@w3.org

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> Yes, we'd like to be close to evolving standards as well, but it's tough
> with a small group of developers, who all work on it when they get the time.
Sure, I know...


> No, though we can always add anything that has a good use case going for
> it.  I suppose that the only real difficulty would be in how to handle
> non-numeric bindings for the variables the function acts on.  Shouldn't
> be too hard though.

yes, like in SQL sum/avg(string x) is not meaningful, but min or
max(string x) means the min/max occurance of x in a group.

A SPARQL aggregate query could look like:

SELECT ?year AVG(?spots) WHERE {
	?s a :SunspotObservation .
	?s :spots ?spots .
	?s :year ?year .
} GROUP BY (?year) .

...remains the question where to put the group by clause and the AVG().


> I'll talk to one of the guys who did the most recent optimization work
> about getting some documentation for this...

this whould be interesting. In our case, we will have a cost-based model
possibly including intra-query parallelism when distributing queries
across nodes. This would mean optimization based on reponse time and not
resource consumption.


> Mulgara currently allows for distributed queries.  What I mean by this,
> is that it lets you select from graphs on more than one server.  You can
> specify that each pattern get matched against graphs that you specify
> (on whichever server), or you can specify an expression of
> unions/intersections of graphs on different servers which the entire
> WHERE clause will be matched against.  This isn't optimized for network
> traffic, but I'm expecting that my company will let me implement that on
> work time later this year.

interesting, although doing this a second time [2] may really be
frustrating  (you've got my compassion ;-)
Do I have to setup Mulgara on each node or is it working like with
SPARQL-protcol enabled-endpoints?

What I really miss and what may really degrade the SPARQL protocol [1]
is some kind of cursors.

regards,
Andy


[1] http://www.w3.org/TR/rdf-sparql-protocol/
[2] http://gearon.blogspot.com/


- --
- ----------------------------------------------------------------------
Dipl.-Ing.(FH) Andreas Langegger
Institute for Applied Knowledge Processing
Johannes Kepler University Linz
A-4040 Linz, Altenberger Straße 69
> http://www.faw.at
> http://www.langegger.at
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Received on Friday, 27 April 2007 14:24:41 GMT

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