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Re: Booleans as the degenerate case of variable binding results

From: Simon Raboczi <raboczi@tucanatech.com>
Date: Tue, 22 Jun 2004 10:25:53 -0400
Message-Id: <11A3BC78-C458-11D8-A9DC-000A95C5686E@tucanatech.com>
To: public-rdf-dawg@w3.org


On 18/06/2004, at 7:39, Kendall Clark wrote:

> I can think of several use cases where what I care about isn't the
> particular answers -- the actual string comprising someone's email
> address -- but *that* some graph has "an email address".

If we have anything resembling a SELECT clause that can be used to 
project away variables, you get this effect by projecting away ALL the 
variables.  Once the projection operation finishes removing duplicates, 
you end up with either true or false depending whether there were any 
solutions or not.

> Or, for example, I don't care about the values of foaf:knows 
> predicates, I
> just want to know whether some FOAF resource contains more than 8 of
> them.

I think this is an entirely different kind of query.  Rather than "Can 
this query be satisfied? I don't care about the particular variable 
bindings required to satisfy it.", it's "Calculate a particular 
variable binding ?x = (count > 8) whose value just happens to be a 
boolean".  In this case you certainly will get an explicit literal 
value back, presumably datatyped using XSD.  However, it's just a 
normal variable binding expression.
Received on Tuesday, 22 June 2004 10:26:31 GMT

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