Hi again Saikat,
> a WeightedPath in the neo4j world is a path that contains weights between
> nodes, in the realm of calculating the shortest path using for example the
> Dijkstra Algorithm the path weights (in this case the distances) are all
> summed up and the path with the minimum total weight is the one returned.
> Here's an example using the weightedpath in the neo4j world
> (http://components.neo4j.org/neo4j-graph-algo/). In my graph all paths have
> weights corresponding to length, that being said how do I then convert the
> data returned by Gremlin to a datastructure that represents a list of
> WeightedPath objects. I need this datastructure to be returned through json
> back to the client.
In the world of Gremlin there is no such thing as "calling a shortest path
algorithm," "calling an eigenvector algorithm," etc. See the rational behind
this idea here:
http://markorodriguez.com/2011/02/08/property-graph-algorithms/
With that said, in Gremlin you have to write your own shortest path from the
atomic traversal primitives provided (i.e. the steps). Here is a Wiki document
on doing depth-first, breadth-first, and hybrid models of graph traversal in
Gremlin:
https://github.com/tinkerpop/gremlin/wiki/Depth-First-vs.-Breadth-First
Using the constructs there, you can write a shortest path that is tailored to
your particular domain model. For example, given the domain model articulated
here:
https://github.com/tinkerpop/gremlin/wiki/Defining-a-More-Complex-Property-Graph
(edges have weights in this graph)
I demonstrate how to get the sum of the weights of each path here:
http://paste.pocoo.org/show/340560/
In terms of creating a WeightedPath object for Neo4j Server reasons, you can
just do plain old Java in Gremlin. Again, Gremlin is a DSL in Groovy and thus,
Java. I don't know the specifics of how to create a WeightedPath object or even
if Neo4j allows you too (?protected constructor?).
Anywho, I think what I have provided gives you enough details for how to sum
weights along paths in a graph...
I can help you more if you need something specific to your domain model --- or
again, if you give me a specific problem aimed at this domain model:
https://github.com/tinkerpop/gremlin/wiki/Defining-a-More-Complex-Property-Graph
I will make it a Gremlin recipe in the Gremlin Cookbook and you can adapt it as
need be for your domain model.
Also, feel free to ping me personally so we don't flood the Neo4j list if you
want more specific help. Or, you can always post to:
http://groups.google.com/group/gremlin-users
Thanks,
Marko.
http://markorodriguez.com
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SIDE NOTE:
Another thing TinkerPop could provide is something like this:
ShortestPath.evaluate(g.v(1), g.v(2),
outE('followed_by').inV[[type:'A']]).paths
In other words, while not providing full control, generic path descriptions
could be provided to such "high level" graph algorithms.
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