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