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

On 6/15/2015 15:42, Peter F. Patel-Schneider wrote:
> 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. 

But we assert that engines must go from left to right (just like with && 
in any programming language), so the second case cannot happen.

Do you have any other example of non-determinism?

>>> 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?

I was just thinking out loud. This is not worked out yet, but I think it 
improves flexibility in any case.

HTH
Holger

Received on Monday, 15 June 2015 05:50:41 UTC