Re: SPARQL 1.1 Query erratum

Hey Steve

Maybe I'm being dense because it is too early in the morning here but I
don't see this (with this specific example at least)

Translating to the || form we get:

((RAND() < 0.5) = true) || ((RAND() < 0.5) = false)

Surely that is still always true?

The (RAND() < 0.5) portion non-deterministically returns true/false, so this
means it always returns true for one/both sides of the || (since technically
the two invocations of RAND() could produce values that make both clauses
evaluate to true). Thus in this example the two forms are equivalent even
with the non-deterministic LHS.

I can believe that there may be cases where the || transformation does
produce different results but can't come up with one off the top of my head.
Do you have an actual worked example of a non-deterministic LHS that
demonstrates that the || transformation does not hold?

Rob

From:  Steve Harris <steve.harris@garlik.com>
Date:  Tuesday, May 7, 2013 6:32 AM
To:  "public-rdf-dawg-comments@w3.org" <public-rdf-dawg-comments@w3.org>,
Ivan Herman <ivan@w3.org>
Subject:  SPARQL 1.1 Query erratum
Resent-From:  <public-rdf-dawg-comments@w3.org>
Resent-Date:  Tue, 07 May 2013 13:33:30 +0000

> Spotted by one of the guys in Experian.
> 
>     "The IN operator tests whether the RDF term on the left-hand side is found
> in the values of list of expressions on the right-hand side. The test is done
> with "=" operator, which tests for the same value, as determined by the
> operator mapping."
> 
>     "The IN operator is equivalent to the SPARQL expression:
> 
>     (lhs = expression1) || (lhs = expression2) || Š"
> 
>     But that's not true given a non-deterministic lhs, e.g.:
> 
>     (RAND() < 0.5) IN (true, false)
> 
>     Which is always true by my reading of the text, and only true 75% of the
> time by the equivalence.
> 
> Suggest the following text for the errata:
> 
>     <div class="entry">
>       <p><span style="font-weight: bold;"><a
> id="errata-query-3">errata-query-3</a></span></p>
>       <p>Report: <a href="">this mail...</a></p>
>       <p>In the <a
> href="http://www.w3.org/TR/sparql11-query/#func-in">definition of the IN
> operator</a>, the <tt>(lhs = expressionN)</tt> equivalence should be
> downgraded to an illustration, as the equivalence doesn't hold for a
> non-degterministic lhs.</p>
>     </div>
> 
> Cheers,
>    Steve
> 
> -- 
> Steve Harris
> Experian
> +44 20 3042 4132
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