Workflow for loading RDF graph data into Giraph
Issue Type: New Feature
Reporter: Dan Brickley
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;
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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