Re: Attempting (vainly?) to change the subject was: Blank nodes must DIE! [ was Re: Blank nodes semantics - existential variables?]

Le 29/07/2020 à 18:52, Patrick J Hayes a écrit :
> 
> 

[skip]

> Ahem. https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3199260

Yes. It's important to differentiate between "there is nothing for X" 
and "there is no *standard* for X". And also differentiate between 
"there is something for X" and "there is a *standard* for X".

In this case, there is a well documented formal semantics for Named 
Graphs, namely the one that Pat references. It also has the privilege to 
be the first published formal semantics of Named Graphs.

However, not only "Pat's Named Graph semantics" (I'll use this term to 
denote the semantics defined in Carroll et al.'s paper, that is, the one 
that Pat references) is not standard, but it also isn't the only one 
formal semantics for Named Graphs.

If a document D1 contains:

<x> {
   <Superman> <kissed> <LoisLane> .
   <Superman> owl:sameAs <ClarkKent> .
}

does it say the same thing as document D2:

<y> {
   <Superman> <kissed> <LoisLane> .
   <Superman> owl:sameAs <ClarkKent> .
}

? Or, does D1-union-D2 entails "<x> owl:sameAs <y>".

In Pat's Named Graph semantics, it does not. There are good reasons for 
this, which are explained in Carroll et al.'s paper. Yet, there are also 
good reasons (arguably) to use Named Graphs with the intent that D1 is 
equivalent to D2, or that it entails that D1-union-D2 entails "<x> 
owl:sameAs <y>".

Also, if D3 says:

<x> {
   <ClarkKent> <kissed> <LoisLane> .
}

then, in Pat's Named Graph semantics, it is not the case that D1 entails 
D3. Yet, there are good reasons (arguably) to use Named Graphs with the 
intent that D1 entails D3.

There are ways of defining a formal semantics for Named Graphs such that 
D1 entails D2, or that D1 entails D3, or both.

These different ways of interpreting Named Graphs (and more generally 
RDF Datasets) have been discussed ad nauseam in the RDF 1.1 Working 
Group. The group published a note about these options 
(https://www.w3.org/TR/rdf11-datasets/), that I authored. Although I 
authored it, it is not supposed to reflect my personal view on the 
topic. It is meant to reflect the state of the discussions within the 
working group, and the extent of the possibilities when it comes to 
interpreting Named Graphs and RDF Datasets.

Now, personally, I have my preference. I would prefer that D1 entails 
D3, and I think that Pat's Named Graph semantics could be encoded using 
a different data structure similar to a "named graph literal".

For instance:

<alice> <likes> "<bob> {<Superman> <kissed> <LoisLane> . <Superman> 
owl:sameAs <ClarkKent>}"^^pat:NGSemantics .
<bob> {
   <Superman> <kissed> <LoisLane> .
   <Superman> owl:sameAs <ClarkKent>
}

would entail:

<bob> {
   <ClarkKent> <kissed> <LoisLane> .
}

but would not entail:

<alice> <likes> "<bob> {<ClarkKent> <kissed> <LoisLane> 
.}"^^pat:NGSemantics .

nor:

<alice> <likes> "<nick> {<Superman> <kissed> <LoisLane> . <Superman> 
owl:sameAs <ClarkKent>}"^^pat:NGSemantics .


Opinions may vary. (huho, I think I opened another big can of worms here...)
-- 
Antoine Zimmermann
ISCOD / LSTI - Institut Henri Fayol
École Nationale Supérieure des Mines de Saint-Étienne
158 cours Fauriel
42023 Saint-Étienne Cedex 2
France
Tél:+33(0)4 77 42 66 03
Fax:+33(0)4 77 42 66 66
http://zimmer.aprilfoolsreview.com/

Received on Wednesday, 29 July 2020 20:48:18 UTC