Re: do Property Graphs always assert annotated arcs?

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?

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...
>
> [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 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...
>
> [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 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?
>> >>
>> >
>>
>