Re: Why does RDF* allow triples as objects?

On 04/09/2019 14:33, thomas lörtsch wrote:
>> On 3. Sep 2019, at 22:03, Olaf Hartig <> wrote:
>> Richard,
>> On tisdag 3 september 2019 kl. 14:06:31 CEST Richard Cyganiak wrote:
>>>> On 2 Sep 2019, at 17:37, Olaf Hartig <> wrote:
>>>> The reason why I defined RDF* in the way I did (i.e., allowing triples not
>>>> only in the subject position but also in the object position) was based
>>>> on several thoughts.
>>>> One of which was along the same lines of William's comment. Now, regarding
>>>> your response to this comment, I don't think that introducing the possible
>>>> asymmetry regarding the use of triples within RDF* triples can be
>>>> justified by the fact that RDF has the same kind of asymmetry for
>>>> literals.
>>> You appeal to a symmetry that is absent from RDF to justify a symmetry in
>>> RDF*.
>> I don't think so. I appeal to a symmetry that gives users of the RDF*-specific
>> features the greatest possible flexibility, which is independent of whether
>> symmetry of other aspects of RDF is present or absent from RDF.
> RDF is symmectric with respect to IRIs and asymmetric with respect to literals. In my intuition RDF* (nested) statements are a lot more similar to IRIs than they are to literals (especially, but not only in PG mode). Therefor I lean to symmmetry with respect to the principle of least surprise.

I think of them as literals.  An IRI is dereferenced (conceptually). 
Literals aren't and the <<>> completely describes the triple.

That said, closer to "generalized RDF" [1] is a better base for 
discussion of abstract data model and then consider restrictions for 
syntax of convenient forms.


>>> I can think of clear use cases for some of these items
>>> that are difficult to address with RDF* as it stands, while I have trouble
>>> thinking of a use case that requires triples-as-objects.
>> There may be use cases that require describing a relationship between two
>> triples, which can be captured naturally by an RDF* triple that has one of the
>> triples as its subject and the other as object.

Can we capture the use case please?

In PG, don't edges have attributes, not edges-on-edges?, which (I guess) 
would be RDF*-triples with literals as objects.



Received on Thursday, 5 September 2019 17:46:25 UTC