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Re: extensibility

From: Eric Prud'hommeaux <eric@w3.org>
Date: Mon, 21 Jun 2004 12:13:44 -0400
To: "Seaborne, Andy" <andy.seaborne@hp.com>
Cc: public-rdf-dawg@w3.org
Message-ID: <20040621161329.GD20051@w3.org>
On Mon, Jun 21, 2004 at 04:06:23PM +0100, Seaborne, Andy wrote:
> Eric,
> The extensibility mechanism is by naming a feature set in the query.  I
> think having named sets of features is a good idea, rather than always
> having just a feature-by-feature naming.  It might be useful to be able to
> enquire of a query processor what feature sets it supports.
> There seem to be two usages:
> 1/ Want to ensure a number of queries can be executed, the early ones may
> not need a given extension so the app wants to knowion advance it wil be OK.
> To do this, it needs to ask before a query is submitted.

Good point. That technique could be used to identify server that can
or will do inferencing for you.

> 2/ In any given query, it is only the fetaures actually used that matter,
> not the whole set (if named).  In this case, can't the query processor
> detemine which features are needed simply by parsing the request?  If so,
> then there is some neatness in declaring features but it isn't necessary is
> it?  Or do required features modify the query/results in some way?

My main goal was to make sure a query server would know if it
understood a request. Two folks could invent the "assert" action (say
one took statements in n3 and another expected p s o) and the server
would either not know which to expect or not even know that there
*was* another one out there.

There may be mutually exclusive extensions. Perhaps the client
wouldn't have thought a lot about its query and not reallize that
there were some conflicts, but I bet it would be apparent to the
person developing the server code. These requests would get a response
from the server indicating the conflict and the client would have to
think harder about what they were trying to ask..

Less importantly, maybe some proxy can do something clever with a
cursory parsing of the query without knowing the full semantics of all
the extensions. But then, maybe not.

> -------- Original Message --------
> > From: Eric Prud'hommeaux <>
> > Date: 21 June 2004 08:59
> > 
> > I've done a bunch of thinking over the weekend about extensibility and
> > how it interacts with streamability. I've prototyped a solution in
> > algae. 
> > Take a peek at the Algae doc on profiles and extensibility [1] and an
> > extension (implemented, but poorly documented at this point) on adding
> > rules to query [2]. It uses and demonstrates the extensibility
> > mechanism. 
> > 
> > [1] http://www.w3.org/2004/05/06-Algae/#extensibility
> > [2] http://www.w3.org/2004/06/20-rules/


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Received on Monday, 21 June 2004 12:13:46 UTC

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