Re: Why nested triples?

> On 19. Feb 2021, at 15:16, Andy Seaborne <andy@apache.org> wrote:
> 
> It does not have to be as either/or.
> 
> An application/sub-system can mask nested embedded triples from a general parser.
> 
> Current use cases are not defining the limit of uses in the future.
> 
> "largely unnecessary" is to me a reason to include them, because we don't know the future use cases and patterns

This seems to me to be as arbitrary an argument as it can possibly get.

Thomas



> - as per Olaf's example.
> 
>    Andy
> 
> On 18/02/2021 22:10, Holger Knublauch wrote:
>> My input:
>> I think nested triples should not be allowed. They are largely unnecessary, will cause extra work and put limitations on the design choices.
>> As an implementer I can say that we don't support nested triples and do not want to (have to) support them.
>> Even in the case that RDF-star introduces a new term type, it would be easy to exclude certain combinations, such as that triple terms cannot be subject, predicate or object of another triple term. Similar restrictions (thankfully) already exist in normal, non-generalized RDF. Such restrictions mean that algorithms that actually use/display/consume RDF have fewer cases to cover, and this will help the adoption of RDF-star in industry.
>> There are in my experience significant downstream costs to users even if it sounds nice, consistent and symmetric from a spec point of view and for those who write low-level algorithms, parsers etc.
>> Holger
>> On 2021-02-19 12:02 am, Antoine Zimmermann wrote:
>>> 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?
>

Received on Friday, 19 February 2021 15:59:28 UTC