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Re: New Terminology Section

From: Martynas Jusevičius <martynas@graphity.org>
Date: Tue, 10 May 2016 07:18:32 +0000
Message-ID: <CAE35Vmy3NYN4LGTv-sUJB2hzvE=3VNPmZuLjrR_HwhjjPoYXDg@mail.gmail.com>
To: Holger Knublauch <holger@topquadrant.com>, RDF Data Shapes Working Group <public-data-shapes-wg@w3.org>
Since SPIN takes an object-oriented view on inheritance, my guess is that
SHACL does the same. I had suggested some time ago that it can be defined
using simple rules (Jena rules in this case):

[constructors: (?class rdf:type rdfs:Class), (?class <
http://spinrdf.org/spin#constructor> ?o), (?subClass rdfs:subClassOf
?class), noValue(?subClass <http://spinrdf.org/spin#constructor>) ->
(?subClass <http://spinrdf.org/spin#constructor> ?o) ]
[constraints: (?class rdf:type rdfs:Class), (?class <
http://spinrdf.org/spin#constraint> ?o), (?subClass rdfs:subClassOf
?class), noValue(?subClass <http://spinrdf.org/spin#constraint>) ->
(?subClass <http://spinrdf.org/spin#constraint> ?o) ]

https://groups.google.com/forum/m/#!msg/topbraid-users/vKkcn_5Esek/4vXFHq6MBQAJ

On Tue, 10 May 2016 at 08:43, Holger Knublauch <holger@topquadrant.com>
wrote:

> On 10/05/2016 14:31, Tom Johnson wrote:
>
>
>
> On Mon, May 9, 2016 at 8:18 PM, Holger Knublauch <holger@topquadrant.com>
> wrote:
>
>> On 10/05/2016 12:30, Tom Johnson wrote:
>>
>>
>>
>> On Mon, May 9, 2016 at 5:29 PM, Holger Knublauch <holger@topquadrant.com>
>> wrote:
>>
>>>
>>>
>>> On 10/05/2016 10:11, Tom Johnson wrote:
>>>
>>> Irene, you say:
>>>
>>> > "Doing more" doesn't create a problem, but, on the other hand, it is
>>> not required.
>>>
>>> I'm really uncertain about this. Couldn't inferring further class
>>> relations (e.g., by using the entailment mechanism included in the spec)
>>> cause different results for basically every operation in SHACL?
>>>
>>>
>>> Can you think of a specific example? sh:entailment would potentially
>>> produce additional triples. But this is the user's choice, and then the
>>> user may expect to see additional validation results...
>>>
>>
>> We seem to be in agreement that inferring additional triples will change
>> results. Examples seem obvious; adding a `subClassOf` statement whose
>> subject is any class referenced in a shape will do the trick, but that's
>> far from the only example.
>>
>> This seems like a problem to me because I don't see that it's clear where
>> triples like `subClassOf` must appear (data graph? shapes graph? any
>> graph?) for a resource to count as a shape, or to match various constraint
>> components.
>>
>>
>> To have an effect on sh:scopeClass and sh:class, the subClassOf triples
>> must be in the data graph.
>>
>
> Is this stated somewhere in the current spec? I haven't been able to find
> it, if so.
>
>
> For sh:scopeClass, Section 2.1.2:
>
> "Note that, according to the SHACL instance definition, all the
> rdfs:subClassOf declarations must exist in the data graph."
>
> For sh:class the same rules apply as for every other constraint component
> - it looks for triples in the data graph. We could theoretically repeat
> this everywhere, e.g. for sh:minCount, but at some stage this should be
> clear. However, given that multiple people have run into this question
> recently, I have just added a clarification to sh:class:
>
>
> https://github.com/w3c/data-shapes/commit/4c0b8f1cbc8faa09624d1a35fc0a8ef564af09b7
>
>
> Also, the question applies equally to cases where the intent is presumably
> that (only?) the data graph counts. For instance: which resources count as
> sh:Shapes?
>
>
> This would have to be in Section 4, but this is currently under revision
> and may be merged with section 2 shortly, so I'll not touch it right now.
> But the intent is that any Shape definition triples such as ex:MyShape
> rdf:type sh:Shape are only relevant if they are in the shapes graph.
>
>
> Note that adding a `subClassOf` triple to a shapes graph to effect
>> validation could be considered a feature; I'm unsure whether that feature
>> is supported.
>>
>>
>> Currently the spec only looks at the data graph.
>>
>>
>> Additionally, `sh:entailment` seems generally under/un-defined. Can
>> inference effect data graphs only? or also shapes graphs? Which triples can
>> be considered by a reasoner and how are inferred triples used by the SHACL
>> semantics?
>>
>>
>> I have just clarified this to the sh:entailment section:
>>
>>
>> https://github.com/w3c/data-shapes/commit/71a9eeaff0317de0cdca6b36500412dabc922f78
>>
>> I am unsure how many people will actually use sh:entailment, so any
>> feedback/requirement may help us add missing details. It is very brief
>> right now, indeed.
>>
>
> I think some clear definition is called for; otherwise, I would simply
> remove the feature; is there a functional difference between entailment (in
> this case) and providing a mechanism for the user/engine to add arbitrary
> triples to the data or shapes graph during pre-processing? This could be a
> simpler way to think of the problem.
>
>
> Regardless of whether sh:entailment exists, any implementer or engine
> already has any freedom to modify the graphs prior to sending them to the
> SHACL engine. This is outside of the SHACL language. The rest needs to be
> decided by the WG, for which I cannot speak here.
>
>
> Holger
>
>
>
>
> - Tom
>
>
> Holger
>>
>>
>>
>> Some of my other concerns about the specifics of `class` and `instance`
>> definitions seem to be in the process of being fixed up; from a quick
>> reading of the latest editor's draft, this is looking promising.
>>
>> - Tom
>>
>>
>>> Thanks, i
>>> Holger
>>>
>>>
>>>
>>>
>>> In lieu of a repeat of previous conversations, I'll just say: For me, as
>>> an implementer in waiting, this is a huge problem. On last reading, very
>>> little seemed unambiguously defined.
>>>
>>> - Tom
>>>
>>> On Mon, May 9, 2016 at 12:14 PM, Irene Polikoff <irene@topquadrant.com>
>>> wrote:
>>>
>>>> Karen,
>>>>
>>>> As I understand it, RDFS inferencing is one way to address this.
>>>> However,
>>>> RDFS inferencing would do more than what is specified here. "Doing more²
>>>> doesn¹t create a problem, but, on the other hand, it is not required.
>>>>
>>>> Another way to address this is to run a query as follows:
>>>>
>>>> SELECT ?resource
>>>> WHERE {
>>>>
>>>> ?class rdfs:subClassOf* example:Class1 .
>>>> ?resource a ?class .
>>>>
>>>> }
>>>>
>>>> Running this query would not change any graphs. As an aside, RDFS
>>>> inferencing is also often done without modifying any graphs. Inferences
>>>> are calculated on the fly when users/systems query data without any
>>>> materialization of inferred triples. At least, this is how triple stores
>>>> that support RDFS inferencing typically work.
>>>>
>>>> Does your concern have to do with where the rdfs:subClassOf triples come
>>>> from - would they exist in the data graph, would they exist in the
>>>> shapes
>>>> graph? They could be in either. If no subclass triples are there, then
>>>> the
>>>> first triple match simply binds ?class to example:Class1 and the query
>>>> result is the same as if we were only looking for nodes that are
>>>> connected
>>>> to example:Class1 via rdf:type link.
>>>>
>>>> It doesn¹t seem to be a role of SHACL to mandate where these triples
>>>> should be located. If they are available in either of the graphs, a
>>>> SHACL
>>>> engine should take them into account. If they are not available, than it
>>>> doesn¹t take them into account.
>>>>
>>>> In our experience, users typically put the subclass triples into the
>>>> shapes graph. At the same time, they need flexibility to do whatever
>>>> fits
>>>> their architecture and processes.
>>>>
>>>>
>>>> Irene Polikoff
>>>>
>>>>
>>>> On 5/9/16, 1:47 PM, "Karen Coyle" <kcoyle@kcoyle.net> wrote:
>>>>
>>>> >Type
>>>> >The types of a node are its values of rdf:type as well as the
>>>> >superclasses of these values.
>>>> >
>>>> >This conflates two different relationships: the relationship of a
>>>> >subject to a class (as defined in RDF/RDFS), defining the subject as an
>>>> >instance of the class; and the sub-/super-class relationships between
>>>> >classes. I dont' see how this can be achieved without inferencing.
>>>> >
>>>> >If we assume some pre-processing of the data graph to include the
>>>> >superclasses, then type is precisely as it is defined in RDF - there
>>>> are
>>>> >just more type statements in the graph.
>>>> >
>>>> >As stated, this is quite an expansion of the meaning of type. In
>>>> >addition, it appears to require modifications to the data graph to
>>>> >include the super classes of each class (presumably up to and including
>>>> >rdfs:Resource).
>>>> >
>>>> >I think it would be best if SHACL defined the shape and data graphs as
>>>> >immutable, thus expecting that all operations read but do not modify
>>>> the
>>>> >graphs. I thought we had come to that conclusion.
>>>> >
>>>> >kc
>>>>
>>>>
>>>>
>>>>
>>>
>>>
>>> --
>>> -Tom Johnson
>>>
>>>
>>>
>>
>>
>> --
>> -Tom Johnson
>>
>>
>>
>
>
> --
> -Tom Johnson
>
>
>
Received on Tuesday, 10 May 2016 07:27:27 UTC

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