Re: do Property Graphs always assert annotated arcs?

Hi Pierre,

Just a quick response from a representative "property graph" user. I have
not been active on this list so far, and actually mistook your email for a
gremlin-users post. So let me just say what I would have said.

First of all, property graph frameworks are usually not prescriptive about
semantics, so your property-qualified edge "means what you want it to
mean". At the same time, it is generally not the case that an edge
qualified with a property like "since" would be considered to be asserted,
independently of the property. A canonical example is the TinkerPop toy
graph <http://tinkerpop.apache.org/docs/current/reference/#graph-computing>,
which has a "weight" property on each edge. The edge created{peter, lop}
has a weight of 0.2, which basically means that the statement "Peter is a
creator of LOP" is a non-assertion. I read your :since and :until example
exactly as you do: the statement spouse{alice, bob} is asserted
conditionally on a logical point in time.

Josh


On Thu, Aug 29, 2019 at 8:36 AM Pierre-Antoine Champin <
pierre-antoine.champin@univ-lyon1.fr> wrote:

> Hi all,
>
> here is a question for those on the list who have discussed more than I
> have with Property Graph users.
>
> There seem to be a consensus here that in PG, arcs with metadata are
> asserted at the same time as they are annotated. This is reflected in the
> PG interpretation of RDF*, where:
>
>     <<:alice :spouse :bob>> :since 2001-02-03^^xsd:date .
>
> asserts exactly two triples.
>
> But as I understand, PG people are also likely to express things like:
>
>     <<:alice :spouse :bob>> :since 2001-02-03^^xsd:date ;
>         :until 2004-05-06^^xsd:date .
>
> if Alice and Bob eventually got divorced.
> In that situation, the arc <<:alice :spouse :bob>> should *no longer* be
> considered asserted in the graph.
>
> Question: is this scenario a plausible one in a PG context?
>