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https://issues.apache.org/jira/browse/GIRAPH-141?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13403818#comment-13403818
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Alessandro Presta commented on GIRAPH-141:
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Eli, we agree on the definition of multigraph: a graph that can have parallel
edges.
As you say, we could just use a container type for E, but what gets tricky then
is dealing with edge removal requests: what identifies an edge, once we allow
for parallel ones? Clearly not the value, as we can have parallel edges with
the same value (this may or may not be useful depending on the problem).
All this to say: this issue pushes the limits of our current model. Let's
brainstorm more. It would be interesting to know a few real use-cases (taking a
look at RDF now).
> multigraph support in giraph
> ----------------------------
>
> Key: GIRAPH-141
> URL: https://issues.apache.org/jira/browse/GIRAPH-141
> Project: Giraph
> Issue Type: Improvement
> Components: graph
> Reporter: André Kelpe
> Assignee: Alessandro Presta
>
> The current vertex API only supports simple graphs, meaning that there can
> only ever be one edge between two vertices. Many graphs like the road network
> are in fact multigraphs, where many edges can connect two vertices at the
> same time.
> Support for this could be added by introducing an Iterator<EdgeWritable>
> getEdgeValue() or a similar construct. Maybe introducing a slim object like a
> Connector between the edge and the vertex is also a good idea, so that you
> could do something like:
> {code}
> for (final Connector<EdgeWritable, VertexWritable> conn: getEdgeValues(){
> final EdgeWritable edge = conn.getEdge();
> final VertexWritable otherVertex = conn.getOther();
> doInterestingStuff(otherVertex);
> doMoreInterestingStuff(edge);
> }
> {code}
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