Re: "Multi-Edge Support in RDFn" slides

On 14/12/2022 23:23, Thomas Lörtsch wrote:
>
>> On 14. Dec 2022, at 21:20, Pierre-Antoine Champin<pierre-antoine@w3.org>  wrote:
>>
>> Thomas,
>>
>> note that my argument was not so much about paradoxes, than about self-referential statements (which can be paradoxical or not, but lead to a nasty class of paradoxes).
>>
>> That being said:
>>
>> On 13/12/2022 14:25, Thomas Lörtsch wrote:
>>> How about
>>>
>>>      :A a :Lie .
>>>      << :A a :Lie >> owl:sameAs :Aq .
>>>      :Aq a :Lie .
>>>
>> This example is not self-referential, but could be made self-referential
>>
>>    :A a :Lie.
>>    << :A a :Lie >> owl:sameAs :A.
> Thank you! That’s what I had assumed in my reply to Olaf, but I still wasn’t quite sure.
>
>> So I stand corrected: RDF-star is just as exposed to this kind of paradox as RDFn.
>>
>> Note, however, that this is not a paradox until you define the semantics of owl:sameAs (which is not part of RDF-star's base semantics) and of :Lie. I believe it would be possible to define the semantics of :Lie in a way that would not blow up in our face in the case above -- but I would have to think about it a bit longer.
>>
>>> Doesn’t that overcome RDF-star's syntactic safe guard against paradoxes? And if it does - I’m not a logician, so I’m not sure - aren’t the consequences even worse for RDF-star than for RDFn, as the paradox targets all occurrences of type << :A a :Lie >>, not only one instance as in RDFn’s case.
>> Not, it does not targets all occurrences, because the occurrences are distinctfrom the type -- or, as you phrase it in terms of the type-token distinction: the tokens are distinct from the types. That's why it's called type-token distinction. :-)
Sorry, I didn't quite finish editing that sentence. What I meant was :

No, it does not targets all occurrences, because the occurrences are 
distinct from the triple -- or, as you phrase it in terms of the 
type-token distinction: the tokens are distinct from the types. That's 
why it's called type-token distinction. :-)
> The quoted triple << :A a :Lie >> is by the CG report defined to be a type

No, the CG report does not use the term "type" in the definition. It 
mentions the type-token distinction as an analogy.

A quoted triple is a /term/ 
(https://www.w3.org/2021/12/rdf-star.html#dfn-rdf-star-terms) alongside 
IRIs, literals and blank nodes

>   that means the same everywhere.
just like an IRI, a literal or a blank node means the same everywhere 
(mind you, I'm talking about blank nodes, not blank node identifiers, 
who have a local scope).
>   So everything that is asserted about it is asserted about that type everywhere it is used as term in an assertion (to avoid saying "everywhere it occurs").

rephrasing (to avoid "type" and "occurs"): every statement (asserted 
triple) containing this term makes an assertion about the thing denoted 
by this term (which is the same for all statements/assertions). Yes.

> An occurrence OTOH, as described by RDFn or RDF standard reification or by :X in
>     << :A a :Lie >> :hasOccurrence :X
> occurs only once.

Not sure what you mean by that: "An occurrence (...) occurs only once"

When we talk about an occurrence, it is not the occurrences that occurs! 
When we talk about the occurrences of a word in a phrase, its is the 
words that occur, not the occurrences... Same when we are talking about 
the occurrences of a term in an RDF(-star) graph.

   pa

>   So the paradox would be more "contained". If that makes much of a difference in practice is another question. It seems a little more harmless to me, but a reasoner might be just as upset either way.
>
>
> Thomas
>
>
>>    pa
>>> I haven’t fully understood how the RDF 1.x semantics tackles this topic [0] but as I said before my intuition is that going the way of occurrences (which in my understanding is a more generic term for both instances and subtypes, which - see OWL punning - are rather application specific categories) opens the same venue: interpreting a statement as a concrete occurrence of the type instead of as the type itself (as the RDF-star semantics proposes) separates the two, puts the occurrence in the extension of the type, and thereby avoids paradoxes in the semantics already.
>>>
>>> Thomas
>>>
>>>
>>> [0]
>>> https://www.w3.org/TR/rdf-mt/#technote

>>>
>>>
>>>
>>>
>>>> On 9. Dec 2022, at 08:15, Pierre-Antoine Champin<pierre-antoine@w3.org>
>>>>   wrote:
>>>>
>>>> Thanks Souri,
>>>>
>>>> I added a link to the slides in the minutes of the call where you presented them.
>>>>
>>>> https://www.w3.org/2022/11/17-rdf-star-minutes.html
>>>>
>>>>
>>>> A few remarks about slides 8 and 9:
>>>> - what you call semantics in these slides is more related to the RDF abtract syntax [1] than the RDF semantics [2]. The former is about structural elements of RDF (IRIs, triples...) while the second is about the "things in the world" that the RDF graph is about.
>>>>
>>>> - In those slides, I see no constraint about preventing triples to talk about themselves (which the CG report explicitly forbids [3]). This allows for something like
>>>>
>>>>    :t1 a :Lie (:t1).
>>>>
>>>> or, even more tricky to detect
>>>>
>>>>    :t2 a :Truth (:t1).
>>>>    :t1 a :Lie (:t2).
>>>>
>>>> This kind of paradoxes may be tricky to model in terms of semantics....
>>>>
>>>>    pa
>>>>
>>>> [1]
>>>> https://www.w3.org/TR/rdf11-concepts/

>>>>
>>>> [2]
>>>> https://www.w3.org/TR/rdf11-mt/

>>>>
>>>> [3]
>>>> https://www.w3.org/2021/12/rdf-star.html#concepts

>>>>    "Note also that, by definition, an RDF-star triple cannot contain itself"
>>>>
>>>> On 03/12/2022 00:21, Souripriya Das wrote:
>>>>
>>>>> Attached a revised version of the RDFn slide deck [1] that includes
>>>>>  • (slide 8) new slide titled "RDFn Semantics: Essentials, in a few words"
>>>>>  • (slide 9) corrected slide titled "RDFn Semantics: Essentials Beyond RDF" that now states that TI INTERSECT TE need not be an empty set and shows the corrected diagram
>>>>>  • (slide 14) new slide titled "Enabling Explicit Naming in RDF-star, Serializations, and SPARQL-star"
>>>>> Thanks,
>>>>> Souri.
>>>>>
>>>>> [1]
>>>>> https://lists.w3.org/Archives/Public/public-rdf-star-wg/2022Nov/att-0016/RDFn_WG_Slides.pdf

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>>>>
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