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From "Paolo Castagna (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (GIRAPH-170) Workflow for loading RDF graph data into Giraph
Date Thu, 05 Apr 2012 19:08:24 GMT

    [ https://issues.apache.org/jira/browse/GIRAPH-170?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13247542#comment-13247542
] 

Paolo Castagna commented on GIRAPH-170:
---------------------------------------

bq. we may want to consider therefore adding backlinks

Yep. I'd like to better understand what people currently do if they need incoming and outgoing
links for their processing.
An adjacency list can be constructed listing incoming (a.k.a. backlinks) as well as outgoing
links, in one MapReduce job.

Input:

s1 -p1-> o1
s1 -p2-> o2
s1 -p2-> o3
s2 -p1-> s1
s2 ...

Output (adjacency list):

s1 (out: p1 o1) (out: p2 o2) (out: p2 o3) (in: s2 p1)
s2 ...

Whether it is better to do it this way or have support from the Giraph APIs avoiding an initial
MapReduce job to construct the adjacency list, I do not know yet.
                
> Workflow for loading RDF graph data into Giraph
> -----------------------------------------------
>
>                 Key: GIRAPH-170
>                 URL: https://issues.apache.org/jira/browse/GIRAPH-170
>             Project: Giraph
>          Issue Type: New Feature
>            Reporter: Dan Brickley
>            Priority: Minor
>
> W3C RDF provides a family of Web standards for exchanging graph-based data. RDF uses
sets of simple binary relationships, labeling nodes and links with Web identifiers (URIs).
Many public datasets are available as RDF, including the "Linked Data" cloud (see http://richard.cyganiak.de/2007/10/lod/
). Many such datasets are listed at http://thedatahub.org/
> RDF has several standard exchange syntaxes. The oldest is RDF/XML. A simple line-oriented
format is N-Triples. A format aligned with RDF's SPARQL query language is Turtle. Apache Jena
and Any23 provide software to handle all these; http://incubator.apache.org/jena/ http://incubator.apache.org/any23/
> This JIRA leaves open the strategy for loading RDF data into Giraph. There are various
possibilites, including exploitation of intermediate Hadoop-friendly stores, or pre-processing
with e.g. Pig-based tools into a more Giraph-friendly form, or writing custom loaders. Even
a HOWTO document or implementor notes here would be an advance on the current state of the
art. The BluePrints Graph API (Gremlin etc.) has also been aligned with various RDF datasources.
> Related topics: multigraphs https://issues.apache.org/jira/browse/GIRAPH-141 touches
on the issue (since we can't currently easily represent fully general RDF graphs since two
nodes might be connected by more than one typed edge). Even without multigraphs it ought to
be possible to bring RDF-sourced data
> into Giraph, e.g. perhaps some app is only interested in say the Movies + People subset
of a big RDF collection.
> From Avery in email: "a helper VertexInputFormat (and maybe VertexOutputFormat) would
certainly [despite GIRAPH-141] still help"

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