On 30/01/16 14:24, Jörn Hees wrote:
Hi,
What was RDFLib producing?
VALUES (?x ?ys ?zs) {
(3 UNDEF 15)
(5 UNDEF 25)
(2 6 UNDEF)
}
Both are right, though the Virtuoso one is pragmatically more useful in this specific case. There
is no one "right" in general when SAMPLE is involved. Aggregation calculation retains
errors and ?z of UNDEF is an error. SAMPLE picks any value from the choices, and at that point,
errors are "values". See ListEval.
I understand that sample can pick an arbitrary value from its choices.
When it comes to error cases though, it seems this causes confusion as people
might not expect an UNDEF to be a solution if there are other values to pick
from... (undef has to be picked: (5 UNDEF 25) vs. can pick an actual value: (2
6 10)).
As you put it yourself it's pragmatically more useful, so would it hurt to put
a preference like that into the standard?
The v1.1 standard is now fixed - but good suggestion for a prospective
change. I've added it to the errata document, linked to your report,
which is the best I can do.
https://www.w3.org/2013/sparql-errata#errata-query-16
Changing the recommended behaviour of systems, even if "better", was
something the 1.1 WG was loath to do, and chartered not to in the case
of SPARQL 1.0 -> 1.1. In other words, any system that has faithfully
implemented the standard up to now should be respected and not be impacted.
In the meantime, getting the implementations to agree is the way
forward. If that choice is the same everywhere, then it is a better case
for future errata/clarification.
I have raised JENA-1126 for Jena and proposed a change to pick a defined
value.
Thanks
Andy
In any case it would be cool if there was a small example (like the one above)
that clarifies the behaviour.
Jörn
[JENA-1126]
https://issues.apache.org/jira/browse/JENA-1126
