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From "Dan Brickley (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (GIRAPH-170) Workflow for loading RDF graph data into Giraph
Date Thu, 05 Apr 2012 18:44:24 GMT

    [ https://issues.apache.org/jira/browse/GIRAPH-170?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13247506#comment-13247506
] 

Dan Brickley commented on GIRAPH-170:
-------------------------------------

Another architectural note around RDF:

RDF is basically simple factual data expressed as sets of binary relationships. In that sense
it is a graph directly, already. 

However often RDF describes something that is in a deeper sense also a graph. Common examples
include FOAF, where node and edge types (Person, Document, Group, etc.) can express matrix
of collaboration, social linkage, etc. Or from DBpedia.org, Freebase etc., we have for example
datasets of movies and actors. In the dbpedia case, it's simple enough; a movie node, an actor
node, and a typed link between them. Freebase by contrast, reifies the 'starring' relationship
into another node, ... so you can represent dates, character name etc. This sort of meta-information
(properties of links) is also btw in the BluePrints/Gremlin API.

One point here is that a 'starring' link pointing from a Movie to an Actor, tells us the same,
but in reverse, as what we would have learned from a 'starsIn' link from the Actor to the
Movie. For Giraph we may want to consider therefore adding backlinks so each node is equally
aware of properties pointing both in, and out.

                
> 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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