Re: shapes-ISSUE-129 (existential constraints): Existential constraints should be consistent [SHACL - Core]

On Wed, Mar 16, 2016 at 10:54 AM, Holger Knublauch <holger@topquadrant.com>
wrote:

> On 16/03/2016 17:44, Dimitris Kontokostas wrote:
>
>
>
> On Wed, Mar 16, 2016 at 8:35 AM, Holger Knublauch <
> <holger@topquadrant.com>holger@topquadrant.com> wrote:
>
>> Could you sketch how the SPARQL would look like for sh:equals,
>> sh:notEquals, sh:lessThan? I see no issues with the current definitions,
>> but I may be missing something. Do you have a case where sh:equals and
>> sh:notEquals are not symmetric? To me, notEquals reports the intersection
>> and equals reports violations for all values that are outside of the
>> intersection.
>>
>
> I would define sh:equals as
>
> SELECT $this ($this AS ?subject) $predicate ?object
> WHERE {
>  $this $predicate ?object .
>  $this $equals ?object2 .
>  FILTER (?object != ?object2) .
> }
>
>
> But this would iterate over all combinations, i.e. even for two identical
> sets of 2 values, it would produce violations. In other words, both
> properties could only ever have one value.
>

Good point! so I would adjust the current definition to

SELECT $this ($this AS ?subject) $predicate ?object WHERE { {
  $this $predicate ?object .
  $this $equals [] .
  FILTER NOT EXISTS { $this $equals ?object .
} } UNION {
  $this $predicate [] .
  $this $equals ?object .
  FILTER NOT EXISTS { $this $predicate ?object . }
 } }

added "  $this $equals [] ." & "  $this $predicate [] . " to make sure the
quality is verified only when both properties exist


> I regard these as set-operators.
>
> sh:equals: both sets must be equal
> sh:notEquals: both sets must not be equal, i.e. there are nodes outside of
> either set
> sh:lessThan: all values of set1 must be < all values of set2
>

I agree


> sh:hasValue: the set must include a given value
>

sh:in should be also added i this category then


>
>
> Holger
>
>


-- 
Dimitris Kontokostas
Department of Computer Science, University of Leipzig & DBpedia Association
Projects: http://dbpedia.org, http://rdfunit.aksw.org, http://
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Homepage:http://aksw.org/DimitrisKontokostas
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