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Why nested triples?

From: Antoine Zimmermann <antoine.zimmermann@emse.fr>
Date: Thu, 18 Feb 2021 15:02:11 +0100
To: "public-rdf-star@w3.org" <public-rdf-star@w3.org>
Message-ID: <ef54b71e-a211-34ac-9b4f-12143ec882d1@emse.fr>
The RDF-star syntax allows for arbitrary nesting of triples like so:

<< :s :p << << :a :b :c >> :y :z >> a :nesting .

Why is it so, why is it useful/needed?
There are no examples of nested triples. There are no justifications in 
the spec for allowing this. As far as I know, there are no examples in 
the past documents that defined RDF*. I did not see any use cases 
discussed for them.

However, I have seen discussions that may serve as counter arguments: 
when asked why embedded triples are limited to single triples rather 
than sets of triples, it has been answered that RDF* is used to model 
property-graph-like annotations that only concern one edge at a time. In 
this case, nested triples should not be allowed, using the same 
arguments (as far as I know, it is not possible to nest edge-annotations 
in property graph systems).

Nesting makes parsers more complicated, makes it more difficult to 
define the semantics of the data model as well as of the query language.

If some use cases justify nested triples, then why not use cases justify 
embedded sets of triples?

Also, a question to implementers: do you support nested embedded triples?
Antoine Zimmermann
École des Mines de Saint-Étienne
158 cours Fauriel
CS 62362
42023 Saint-Étienne Cedex 2
Tél:+33(0)4 77 42 66 03
Received on Thursday, 18 February 2021 14:02:27 UTC

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