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Re: Slides for Berlin Data Workshop

From: Gregg Kellogg <gregg@greggkellogg.net>
Date: Tue, 26 Feb 2019 09:01:17 -0800
Cc: public-linked-json@w3.org
Message-Id: <0A452F64-4368-4A45-92BB-D6514D4B2B2D@greggkellogg.net>
To: Antoine Zimmermann <antoine.zimmermann@emse.fr>
> On Feb 26, 2019, at 1:49 AM, Antoine Zimmermann <antoine.zimmermann@emse.fr> wrote:
> 
> Hello,

Hi Antoine,

> This is my first email to the JSON-LD CG mailing list, so let me introduce myself: I am Antoine, working on semantic web technologies since 2004 as a researcher. I participated in the RDF 1.1 working group, quite actively, where my primary interest was RDF semantics.
> 
> Concerning your slides, Gregg, on slide 2, you say "The only reasonable interpretation of graphs named via blank node (...) is that the blank node denotes the graph it names".
> 
> Graph names can be interpreted in many ways, lots of which are considered reasonable by those who advocate them.
> 
> In fact, the very people who introduced the concept of named graphs (Carroll et al. in 2004) defined a formal semantics according to which an RDF interpretation I satisfies ("conforms to", in their words) a named graph (n,g) iff I(n) = (n,g), that is, the name is interpreted as the named graph *pair*, not the graph.
> 
> Many people have used the idea of quads (that can be seen as a syntactic variation of the concept of named graphs) in very different ways, some of which are implemented in triple stores (e.g., spatio-temporal triple store Strabon).
> 
> In any case, defining the meaning of a JSON-LD document is not part of the JSON-LD group's mission. JSON-LD defines how to map a JSON-based format to the abstract RDF structures, then people interpret it as they want, possibly following other specs like RDF Semantics, OWL, SWRL, or N3logic.

My understanding of the rationale behind the reasoning that the names of named graphs do not denote those graphs is for the URI case. It’s true, what you say, that there are numerous deployed systems (for better or worse) that have their own interpretation. However, my position is that blank nodes allow for a different interpretation, as they can have no meaning outside of any given serialization. This allows us to allow for the interpretation that blank node names of named graphs _could_ actually denote those graphs. This is evident in the usage of anonymous named graphs in specs such as Verifiable Credentials [1].

In any case, these are my own opinions, and not those of either the JSON-LD WG or CG. The purpose of the workshop is to lay out areas for future development, and I think such an interpretation would help bring RDF into line with Notation3 formula and relate to actual real-world use.

> Similarly, slide 5 is not about "Reasoning in JSON-LD": it is explaining how to map N3 formulas to JSON-LD. Then people can decide to interpret JSON-LD documents as N3, following slide 5 representation, and do *N3 reasoning*, not "JSON-LD reasoning". They could also just map this representation to a normal RDF dataset and apply other kinds of reasoning.

Yes, I should be more explicit, it is about a way to extend the RDF model to allow for a syntax to describe things that can later be interpreted for reasoning. I’d like to see some of the N3 reasoning concepts be made more broadly applicable to an extended RDF dataset; one which allows universally quantified variables as resources.

At this time, although N-Quads and TriG _can_ represent what seems as graphs as suitable for triple resources, only JSON-LD provides a reasonable (IMHO) way to state this; Sandro had another idea for a TriG-like language that could have done this as well, which we briefly explored at the end of the RDF 1.1 WG, but abandoned; perhaps it, or something like it, needs to be reconsidered.

Gregg

[1] https://w3c.github.io/vc-data-model/
> 
> Best,
> --AZ
> 
> Le 23/02/2019 à 23:50, Gregg Kellogg a écrit :
>> The format for the Berlin Data Workshop [1] remains unclear, but I’ve prepared just a couple of slides to describe one way in which Anonymous Named Graphs in JSON-LD could support the property graph use case.
>>> https://json-ld.org/presentations/JSON-LD-Support-for-Property-Graphs/ <https://json-ld.org/presentations/JSON-LD-Support-for-Property-Graphs/>
>> There’s a short overview of new things in JSON-LD 1.1, and as a bonus, a sketch of how Notation3 reasoning might look in JSON-LD. (Hint, we really only need to invent a way to describe universal variables at the syntax level; reasoning should be universal based on obvious projections from Notation 3. The required extensions to RDF Datasets and better description of reasoning semantics are work to be done elsewhere).
>> Gregg Kellogg
>> gregg@greggkellogg.net
>> [1] https://www.w3.org/Data/events/data-ws-2019/schedule.html
> 
> -- 
> Antoine Zimmermann
> Institut Henri Fayol
> École des Mines de Saint-Étienne
> 158 cours Fauriel
> CS 62362
> 42023 Saint-Étienne Cedex 2
> France
> Tél:+33(0)4 77 42 66 03
> Fax:+33(0)4 77 42 66 66
> http://www.emse.fr/~zimmermann/
> Member of team Connected Intelligence, Laboratoire Hubert Curien
> 
Received on Tuesday, 26 February 2019 17:01:44 UTC

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