Re: do Property Graphs always assert annotated arcs?

Olaf,

On Thu, 19 Sep 2019 at 13:02, Olaf Hartig <olaf.hartig@liu.se> wrote:

> (...)
> I think when comparing PGs and RDF/RDF*, it is not so important to
> distinguish whether an edge in a PG--or, more precisely, whatever the
> edge is supposed to represent--can be considered to be asserted or not.
> In PGs, every edge that has attributes (edge properties) exists in the
> graph. There is no way to associate attributes with a non-existent
> edge. In contrast, in RDF, and also in RDF* (assuming SA mode), we can
> make statements about a triple that is not part of the graph itself.
>

Agreed.
But that also means that there is no general way to determine whether a PG
edge should be converted to an asserted RDF triple, or a non-asserted RDF
triple. That makes it difficult to define a generic mapping in that
situation.
From what I gathered, it seems that it might depend:

* on the vocabulary, i.e. the type of the edge (i.e. an edge with type
"city-of-birth' would be considered as always true, while an edge
"married-to" would be time-dependant);
* on the value of some edge-attribute (i.e. an edge "mariied-to" with a
property "until: 2018-03-21" would be considered unasserted)
* on the presence/absence of edge property (i.e. an edge "married-to"
*without* any property "until" would be considered as still valid).

The last point especially worries me, because it relies on a closed world
assumption, while RDF semantics is based on the open-world assumption.

 best