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From Vasiliki Kalavri <vasilikikala...@gmail.com>
Subject Re: [DISCUSS] Graph algorithms for vertex and edge degree
Date Tue, 26 Apr 2016 12:27:35 GMT
Hey Greg,

when we made the initial design for Gelly, we discussed having separate
directed and undirected graph types.
We decided to represent undirected graphs by simply adding the
opposite-direction edges, like Apache Giraph does. I'm not sure whether
that was a good idea, but, back then, it seemed to simplify the design of
the API.
If you think we can improve the API and the usability of Gelly by
introducing separate types, I would love to hear your proposal!

Cheers,
-Vasia.

On 25 April 2016 at 22:49, Greg Hogan <code@greghogan.com> wrote:

> Hi Fabian,
>
> I don't know if this has been looked at. There is discussion of
> BipartiteGraph in FLINK-2254. If Gelly had DirectedGraph and
> UndirectedGraph then the API could stay lean while methods could be tuned
> for the specific graph type. I do like having simple APIs such as DataSet
> and Graph for for interactive use in small scripts or Scala and Python
> shells.
>
> Greg
>
> On Mon, Apr 25, 2016 at 8:46 AM, Fabian Hueske <fhueske@gmail.com> wrote:
>
> > Hi Greg and Vasia,
> >
> > thanks for starting this discussion.
> > I think it is a good idea to update the Gelly roadmap. As Vasia said,
> many
> > items on the list have been implemented and other have been more or less
> > dropped.
> > Also new persons who want to improve Gelly have joint the community while
> > others have become idle.
> > So from my point of view it makes perfect sense to gather the input of
> the
> > community and update the Gelly roadmap.
> >
> > Regarding the specific changes of FLINK-3772, I am usually always in
> favor
> > of performance improvements.
> > How much would the suggested functionality for degree computation
> overlaps
> > with the current methods?
> > Could the current methods be replaced by the more efficient
> implementations
> > or would there be two methods which look very similar and behave almost
> the
> > same?
> >
> > Best, Fabian
> >
> >
> >
> > 2016-04-22 11:00 GMT+02:00 Vasiliki Kalavri <vasilikikalavri@gmail.com>:
> >
> > > Hi all,
> > >
> > > I asked Greg to start a discussion here about FLINK-3771 and
> FLINK-3772,
> > to
> > > make sure we're all on the same page about future Gelly development.
> > >
> > > About a year ago we created the Gelly roadmap [1]. Many of these items
> > have
> > > been implemented and others were researched and either developed
> > externally
> > > or dropped. Graph translators and degree annotations were not in the
> > > roadmap, but I personally think that they are both helpful features and
> > I'm
> > > in favor of adding them to Gelly.
> > >
> > > That said, I find this a perfect timing for revisiting and updating our
> > > Gelly development plans. We should update the roadmap so that it
> reflects
> > > current state and future plans. This way, the community can have a
> clear
> > > picture of what we are working on and what are upcoming features. This
> is
> > > also very important for new contributors. They can always refer to the
> > > roadmap to see what the community is interested in and we can avoid
> > having
> > > people spending their time on obsolete or dropped features. We should
> > also
> > > go through existing JIRAs and clean them up. Several are assigned to
> > people
> > > who have been inactive or might need help.
> > >
> > > In the following days I will go through the roadmap and then start a
> new
> > > thread where we can discuss features and agree on future plans. In the
> > > meantime, it would be great if you give us your view on FLINK-3771 and
> > > FLINK-3772.
> > >
> > > Cheers,
> > > -Vasia.
> > >
> > > [1]: https://cwiki.apache.org/confluence/display/FLINK/Flink+Gelly
> > >
> > > On 21 April 2016 at 18:52, Greg Hogan <code@greghogan.com> wrote:
> > >
> > > > Vasia and I are looking for additional feedback on FLINK-3772. This
> > > ticket
> > > > [0] and PR [1] provides a set of graph algorithms which compute and
> > store
> > > > the degree for vertices and edges.
> > > >
> > > > Degree annotation is a basic component of many algorithms. For
> example,
> > > > PageRank requires the vertex out-degree to evenly divide the vertex
> > score
> > > > among neighbors. The triangle enumeration algorithm in Gelly requires
> > > both
> > > > source and target degree for each edge as an optimization. The
> Jaccard
> > > and
> > > > Adamic-Adar similarities require the target degree for each edge.
> > > >
> > > > As discussed in the ticket, Graph has methods for outDegrees,
> > inDegrees,
> > > > and getDegrees. These are simple but difficult or impossible to use
> > > > efficiently.
> > > >
> > > > Stepping back, I believe algorithms should be composable and reused
> > where
> > > > possible, not only to improve Flink but also to support users.
> > > Implementing
> > > > algorithms as classes rather than Graph methods enables customization
> > and
> > > > optimization such as used here.
> > > >
> > > > One such optimization is CachingGraphAlgorithm which implicitly
> reuses
> > > > DataSets. There is overlap between algorithms. From this ticket,
> > > annotating
> > > > edges with source and target degree on an undirected graph can reuse
> > > vertex
> > > > degree. Local clustering coefficient requires a triangle listing and
> > > global
> > > > clustering coefficient requires a triangle count, there is no need to
> > > > generate the list three times.
> > > >
> > > > Further optimizations include the use of mutable types, reusing sort
> > > order,
> > > > avoidance of coGroup, configurable parallelism, and not unnecessarily
> > > > materializing DataSets. I see all this as the expectation for
> inclusion
> > > in
> > > > Flink.
> > > >
> > > > Greg
> > > >
> > > > [0] https://issues.apache.org/jira/browse/FLINK-3772
> > > > [1] https://github.com/apache/flink/pull/1901/files
> > > >
> > >
> >
>

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