Re: do Property Graphs always assert annotated arcs?

Pierre-Antoine,

On Wed, 2019-09-11 at 19:08 +0200, Pierre-Antoine Champin wrote:
> Thanks Joshua and Jeff, for your answers.
> 
> That confirms my hunch, and reveals that bridging between RDF and PG
> may be more complex than I expected -- and, I think, other people on
> the list expected.
> 
> As I now see it, the existence of an edge in a PG may or may not
> translate to the corresponding triple in RDF. This depends on the
> attributes (if any) of that edge.
> 
> Now, am I right to assume that, in PG land, if the edge has no
> attribute, it will typically be considered asserted, but if I add an
> attribute 'until: 2000-01-01', it is not asserted anymore?

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.

Olaf


> If that's the case, we have an additional problem to represent this
> in RDF land, because we can not infer anything from the *absence* of
> a triple (in this case, the 'until' annotation). We work under the
> open world assumption...
> 
> 
> On Fri 30 Aug 2019, 20:56 Jeff Lerman, <jeff.lerman@invitae.com>
> 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.  RDF/SPARQL provide us at least
> > two ways to handle edges that, as a consequence of their
> > properties, should not be considered to “exist” from the
> > perspective of a query:
> > 
> >  1. Queries can be written to filter out any edges with properties
> > that indicate that they are not valid (e.g., if we are interested
> > in considering/recognizing only edges about marriages in existence
> > at a given time, we should exclude those that have started after
> > that time, or ended before that time)
> > 
> >  2. We can segregate those edges to a named graph which we exclude
> > from SPARQL queries.
> > 
> > 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.  If the extension I have in
> > mind would solve this issue with RDF* though, maybe it is...
> > 
> >     Jeff Lerman AI Scientist Mobile: 510-495-4621 www.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?
> > > >>
> > > >
> > > 
> 
> On Fri 30 Aug 2019, 20:56 Jeff Lerman, <jeff.lerman@invitae.com>
> 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.  RDF/SPARQL provide us at least
> > two ways to handle edges that, as a consequence of their
> > properties, should not be considered to “exist” from the
> > perspective of a query:
> > 
> >  1. Queries can be written to filter out any edges with properties
> > that indicate that they are not valid (e.g., if we are interested
> > in considering/recognizing only edges about marriages in existence
> > at a given time, we should exclude those that have started after
> > that time, or ended before that time)
> > 
> >  2. We can segregate those edges to a named graph which we exclude
> > from SPARQL queries.
> > 
> > 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.  If the extension I have in
> > mind would solve this issue with RDF* though, maybe it is...
> > 
> >     Jeff Lerman AI Scientist Mobile: 510-495-4621 www.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 11:02:33 UTC