Re: ISSUE-22: Proposal based on sh:hasShape

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On 06/13/2015 09:40 PM, Holger Knublauch wrote:
> On 6/12/2015 13:37, Peter F. Patel-Schneider wrote:
>> Changing the order of triples in a shapes or data graph document, or
>> even just running the system again, might end up producing different
>> answers if care is not taken in fleshing out this approach, even in
>> cases where there is no negation or even disjunction.
> 
> Does anyone have a test case that demonstrates such a non-deterministic 
> scenario? AND, OR and XOR all use rdf:Lists and are therefore ordered. 
> sh:valueShape needs to walk through all values of the property, so order 
> shouldn't matter there either. (Apologies if the answer to these
> questions is already somewhere on the mailing list - I found this topic
> hard to follow)

Changing results without negation and without disjunction requires a
(sloppy) short-circuit evaluation on conjunction.  Consider a conjunction
where othe left branch evaluates to true and the right to error..  If the
left branch is evaluated first and short-circuited the result is true.  If
the right branch is evaluated first then the result is error.

>> Picking a bad propagation rule for a "Duh" is going to produce
>> something that I think will be unusable---I don't even know if there is
>> any good set of propagation rules.
> 
> Maybe it would help if we made sh:hasShape return three possible values:
> true, false and unknown. Then the writers of custom SPARQL queries can
> better specify how they are going to treat the undefined cases. I believe
> we need the "unknown" value anyway, e.g. when a JavaScript implementation
> encounters a SPARQL query that it cannot handle.

What are the propagation rules for unknown?  Should there be multiple
unknowns? Should there also be an error value?

> Thanks, Holger

peter

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Received on Monday, 15 June 2015 05:42:43 UTC