Re: do Property Graphs always assert annotated arcs?

Hi Jeff,

On Fri, 2019-08-30 at 11:56 -0700, Jeff Lerman wrote:
> Ah, that’s more in-line with much of the other discussion so far in
> the group.
> 
> I would prefer a model in which it’s not possible to assert a
> property on a non-existent edge.

We have just started a discussion related to this question in another
thread (PG mode and SA mode). It would be nice if you could elaborate
on this preference over there!

> [...]
> I have more to say about ways to handle/leverage named graphs, which
> might make my 2nd suggestion more palatable, but not sure that this
> is the right forum for that.

I think there are other more suitable forums to have discussions
specific to named graphs (unless the topic is also related to the
RDF*/SPARQL* approach).

Best regards,
Olaf


>   If the extension I have in mind would solve this issue with RDF*
> though, maybe it is...
> 
>  Jeff LermanAI ScientistMobile: 510-495-4621www.invitae.com
> 
> 
> On Fri, Aug 30, 2019 at 11:23 AM Olaf Hartig <olaf.hartig@liu.se>
> wrote:
> > Jeff,
> > 
> > These are great examples for cases in which the properties
> > associated with edges in a graph may change over time without
> > affecting the existence of the edges themselves. However, I think
> > Pierre-Antoine's question was focusing on the opposite: does the
> > existence of an edge property always assume the existence of the
> > edge with which it is associated.
> > 
> > Olaf 
> > 
> > -----Original Message-----
> > From: Jeff Lerman <jeff.lerman@invitae.com>
> > To: Joshua Shinavier <joshsh@uber.com>
> > Cc: Pierre-Antoine Champin <pierre-antoine.champin@univ-lyon1.fr>, 
> > public-rdf-star@w3.org
> > Sent: Fri, 30 Aug 2019 18:27
> > Subject: Re: do Property Graphs always assert annotated arcs?
> > 
> > Hi all,
> > 
> > Most of my experience with graphs is with a frame-based approach
> > that most
> > closely resembles a triple-store - not explicitly RDF but close
> > enough.
> > I’ve been exploring both RDF/triple-stores and PGs as candidates to
> > support
> > a new project.  I’ve been following the RDF* discussion with
> > interest.
> > 
> > For what it's worth, I wouldn’t assume that edge-metadata (edge-
> > properties
> > in PG world) must be asserted at the time an edge is asserted. 
> > There are a
> > variety of scenarios in which one might wish to update that
> > metadata, and
> > I’m pretty sure there’s nothing technically preventing such updates
> > in
> > existing PG implementations.  For example, one might:
> > 
> >    - update metadata: alter the value of an already-asserted
> > property:value
> >    pair (e.g., a newer model indicates that the weight of an edge
> > should be
> >    adjusted from 0.2 to 0.8)
> >    - add or subtract metadata: assert (or remove) a value for a
> > property
> >    that was previously un-populated (or populated), to reflect new
> > knowledge
> >    we have about a relationship.  The change could be incremental
> > and need not
> >    affect other properties, so deleting-and-reasserting the edge
> > with all of
> >    the other pre-existing (and unaffected) properties would be
> > inappropriate.
> > 
> > —Jeff
> > 
> > 
> > 
> > [image: email_sig_logo_vert.png]
> > 
> > Jeff Lerman
> > 
> > AI Scientist
> > 
> > Mobile: 510-495-4621
> > 
> > www.invitae.com
> > 
> > [image: email_sig_social_linkedin.png]
> > <https://www.linkedin.com/in/jefflerman/>
> > 
> > 
> > On Thu, Aug 29, 2019 at 10:03 AM Joshua Shinavier <joshsh@uber.com>
> > wrote:
> > 
> > > 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?
> > >>
> > >

Received on Thursday, 19 September 2019 10:47:01 UTC