Re: Nested Graphs - a graph-based proposal

Hi Thomas,

On Wed, 2023-10-25 at 23:43 +0200, Thomas Lörtsch wrote:
> Hi Olaf,
>
> > On 25. Oct 2023, at 22:01, Olaf Hartig <olaf.hartig@liu.se> wrote:
> >
> > Hi Thomas,
> >
> > I tried to understand your proposal but I failed because the notion
> > of a Nested Graph that you aim to introduce is not actually defined
> > in your text. The only thing you provide are several examples that
> > are written using a Turtle-like syntax and that supposedly
> > illustrate how Nested Graphs may be represented in that particular
> > syntax, but these examples don't help me to understand what exactly
> > a Nested Graph is.
>
> this is definitely not a way of putting things that I have much
> experience in, so please tell me if the following makes sense to you:

It is a start, but there are several aspects that need to be elaborated
more on for this to become an actual unambiguous definition. See below.

> A nested graph is a pair consisting of an IRI or a blank node (the
> graph name), and an RDF graph.

Okay, according to this sentence, a nested graph is structurally the
same as a named graph. Fine.

> The name denotes the pair of name and graph.
> Nested graph names are unique within an RDF dataset.
> A nested graph may contain other nested graphs, recursively.

This sentence is a bit too vague for a proper definition. It needs to
be made more clear what exactly "may contain" means.

I assume it means that a nested graph ng = (n,G) may have another
nested graph as the subject or the object of some triple in the RDF
graph of ng. In other words, there may be a triple t=(s,p,o) in G such
that s or o is another nested graph ng' = (n',G').

Is that what you mean?

If so, notice that you are introducing a new kind of term that can be
used in RDF triples (in addition to IRIs, blank nodes, and literals)!

> A nested graph may occur in the default graph as well as in named
> graphs.

"may occur" is also a bit too vague, and should be made more accurate
in a way similar to what I am outlining above for "may contain". But
also notice that another aspect that should be clear from the
definition is whether a nested graph can occur multiple times in the
default graph and/or in the named graphs?

If the answer to the latter question is some form of yes, then how is
this related to requirement that "nested graph names are unique within
an RDF dataset"?

Also, are there any constraints regarding the graph names of nested
graphs that "occur in the default graph as well as in named graphs" and
the names of the named graphs of the dataset?

Best,
Olaf

>
>
> Best,
> Thomas
>
>
> >
> > In comparison, I understand what an RDF triple is because that
> > notion is well defined [1], and so is the notion of an RDF graph
> > [2] and the notion of a Named Graph [3]. Along the same lines, can
> > you provide a definition of the notion of a Nested Graph that you
> > have in mind?
> >
> > Thanks,
> > Olaf
> >
> > [1]
> > https://www.w3.org/TR/rdf12-concepts/#dfn-rdf-triple

> >
> > [2]
> > https://www.w3.org/TR/rdf12-concepts/#dfn-rdf-graph

> >
> > [3]
> > https://www.w3.org/TR/rdf12-concepts/#dfn-named-graph

> >
> >
> >
> >
>

Received on Thursday, 26 October 2023 07:49:39 UTC