- From: Holger Knublauch <holger@topquadrant.com>
- Date: Wed, 16 Mar 2016 16:35:38 +1000
- To: public-data-shapes-wg <public-data-shapes-wg@w3.org>
- Message-ID: <56E8FEBA.60506@topquadrant.com>
Whatever we do with sh:hasValue we need to keep in mind that its
specific term is already used by OWL. If we change the semantics, then
we should rename that property to avoid confusion. I agree it's not nice
to have an implicit sh:minCount>0 here, yet it is convenient and compact
for its common use case in filters.
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.
Thanks
Holger
On 16/03/2016 16:19, Dimitris Kontokostas wrote:
> This is for intuitive understanding of the language. sh:hasValue and
> sh:in are similar to sh:class and sh:classIn
> Users would be confused if e.g. sh:class used the subclass hierarchy
> to check class membership and sh:classIn not.
> I would also find it more intuitive if sh:hasValue was applied only on
> existing values but this is only a personal opinion
>
> On Wed, Mar 16, 2016 at 1:41 AM, Holger Knublauch
> <holger@topquadrant.com <mailto:holger@topquadrant.com>> wrote:
>
> I have trouble voting because I am unclear about is why you want
> to change these things and what the consequences would be. Do you
> believe this is to improve the intuitive understanding of the core
> language, or would those changes lead to simplifications
> elsewhere, e.g. in implementations?
>
> And whatever categorization we are trying to come up with is only
> against the current snapshot of core features (add another one
> like sh:closed and things may fall apart) and we cannot anticipate
> the kinds of constraints people will express with the extension
> mechanism. I think the most natural thing we can do, generally, is
> to group "universal" constraints and "anything else" (which
> corresponds to the current design based on
> sh:NodeValidationFunctions). The "anything else" bucket may have
> to stay homogeneous because there is an almost infinite amount of
> scenarios possible.
>
> Holger
>
>
>
> On 15/03/2016 21:03, Dimitris Kontokostas wrote:
>> I made a proposal with a few variations that can help us resolve
>> this issue faster
>> https://www.w3.org/2014/data-shapes/wiki/Proposals#ISSUE-129:_Existential_constraints
>>
>> On Tue, Mar 8, 2016 at 11:03 AM, Dimitris Kontokostas
>> <kontokostas@informatik.uni-leipzig.de
>> <mailto:kontokostas@informatik.uni-leipzig.de>> wrote:
>>
>> My take on existential constraints is if the sparql
>> definitions contains "WHERE { $this $predicate ?object . ...
>> }" or not
>> if it does it means that the constraint is applied on
>> existing values and does not require the value to exist.
>>
>> Using this definition the list is different
>> non-existential constraints:
>> - sh:class, sh:classIn, sh:datatype, sh:datatypeIn, sh:directType
>> - sh:max/min/In/Exclusive, sh:maxLength, sh:minLength
>> - sh:nodeKind
>> - sh:in
>> - sh:valueShape
>> - sh:closed
>> - sh:uniqueLang
>> - sh:notEquals, sh:lessThan, sh:lessThanOrEquals
>>
>>
>> existential ones:
>> - sh:minCount, sh:maxCount
>> - sh:qualified*
>> - sh:hasValue
>> - sh:equals (sorry, I didn't catch equals before)
>>
>> I didn't mean to include sh:and/or/not as they
>> are different than the other core constraints
>>
>> I suggested to limit them to - sh:minCount, sh:maxCount (and
>> sh:qualified* of course) but if we don't we should keep them
>> consistent
>> sh:hasValue should be consistent with sh:in
>> sh:equals should be consistent with sh:notEquals,
>> sh:lessThan, sh:lessThanOrEquals
>>
>>
>> On Tue, Mar 8, 2016 at 12:48 AM, Holger Knublauch
>> <holger@topquadrant.com <mailto:holger@topquadrant.com>> wrote:
>>
>> Many constraint types indeed apply to "all values" only:
>> - sh:class, sh:classIn, sh:datatype, sh:datatypeIn,
>> sh:directType
>> - sh:max/min/In/Exclusive, sh:maxLength, sh:minLength
>> - sh:nodeKind
>> - sh:in
>> - sh:valueShape
>>
>> These are handled by NodeValidationFunctions in the
>> current draft.
>>
>> Other constraint types are more heterogeneous, and
>> calling them "existential" is IMHO an over-simplification:
>> - sh:and, sh:or, sh:not
>> - sh:closed
>> - sh:equals, sh:notEquals, sh:lessThan, sh:lessThanOrEquals
>> - sh:minCount, sh:maxCount
>> - sh:qualifiedXY
>> - sh:uniqueLang
>> - sh:hasValue
>>
>> Just looking at sh:equals for example, the query is
>> something like
>>
>>
>> SELECT $this ($this AS ?subject) $predicate ?object
>> WHERE {
>> {
>> $this $predicate ?object .
>> FILTER NOT EXISTS {
>> $this $equals ?object .
>> }
>> }
>> UNION
>> {
>> $this $equals ?object .
>> FILTER NOT EXISTS {
>> $this $predicate ?object .
>> }
>> }
>> }
>>
>> i.e. the system will produce violations if the "other"
>> property has a value that isn't present but also
>> vice-versa. It may even fire a violation if there is no
>> value at all, but the other property has values.
>>
>> Coming up with an artificial limitation is likely going
>> to hurt extensions that we cannot anticipate yet, so I
>> believe we must treat them as "arbitrary" constraint
>> types that may do anything they like.
>>
>> I also have seen many use cases of sh:hasValue, esp in
>> filterShapes, so i would be against dropping that.
>>
>> Holger
>>
>>
>>
>>
>> On 7/03/2016 20:49, RDF Data Shapes Working Group Issue
>> Tracker wrote:
>>
>> shapes-ISSUE-129 (existential constraints):
>> Existential constraints should be consistent [SHACL -
>> Core]
>>
>> http://www.w3.org/2014/data-shapes/track/issues/129
>>
>> Raised by: Dimitris Kontokostas
>> On product: SHACL - Core
>>
>> The current core spec defines three existential
>> constraints: sh:minCount, sh:maxCount and sh:hasValue.
>> sh:hasValue requires for a value to exist and match
>> the one supplied in the shape definition.
>>
>> This is not consistent with sh:in which is a
>> variation of sh:hasValue and probably not easy for
>> users to understand the different of sh:hasValue and
>> other constraints e.g. sh:minLength, sh:class, etc
>>
>> I suggest we restrict the core existential
>> constraints to sh:minCount and sh:maxCount only. The
>> rest of the constraints will apply only when there is
>> a value.
>>
>>
>>
>>
>>
>>
>>
>>
>> --
>> Dimitris Kontokostas
>> Department of Computer Science, University of Leipzig &
>> DBpedia Association
>> Projects: http://dbpedia.org, http://rdfunit.aksw.org,
>> http://http://aligned-project.eu
>> Homepage:http://aksw.org/DimitrisKontokostas
>> Research Group: AKSW/KILT http://aksw.org/Groups/KILT
>>
>>
>>
>>
>> --
>> Dimitris Kontokostas
>> Department of Computer Science, University of Leipzig & DBpedia
>> Association
>> Projects: http://dbpedia.org, http://rdfunit.aksw.org,
>> http://http://aligned-project.eu
>> Homepage:http://aksw.org/DimitrisKontokostas
>> Research Group: AKSW/KILT http://aksw.org/Groups/KILT
>>
>
>
>
>
> --
> Dimitris Kontokostas
> Department of Computer Science, University of Leipzig & DBpedia
> Association
> Projects: http://dbpedia.org, http://rdfunit.aksw.org,
> http://http://aligned-project.eu <http://aligned-project.eu/>
> Homepage:http://aksw.org/DimitrisKontokostas
> Research Group: AKSW/KILT http://aksw.org/Groups/KILT
>
Received on Wednesday, 16 March 2016 06:36:13 UTC