HDGS is an abstraction layer (representing time dependent graphs, as well as time series of node or link propeties) on top of HDFS and HBase, to connect the HDGSworkspace - a toolbox for processing, transforming and filtering graphs and networks into the hadoop ecosystem. It is not intendet to be a nother machine learning tool (therefor we have Mahout), but it will combine several existing concepts or tools like: GraphLab, Neo4J, Titan, HAMA, Giraph, Mahout and others in to on place.
https://docs.google.com/a/cloudera.com/document/d/1yb_YB8-ZaoPtqANOrWeV1CGWYHpQAFJSLaTd4DaIQI8/pub