[petern]

Yes, all information models are basically isomorphic. However, Neo4j for instance maintains referential integrity along the relationships, making sure there will never be a relationships without start- or endnode. In a K/V store or document store, there are no guarantees that your IDs pointing to other objects are updated as you change, delete or move the target data. Also, the graph structure is maintained on dics, meaning you can direct pointers on the storage level even in non-cached scenarios, while in a K/V or Document store you need to recreate the graph in memory before being able to do anything with it.

As for special indexes and queries, look at things like http://docs.neo4j.org/chunked/snapshot/cypher-query-lang.htm... expressing patterns and walks in graphs.

You can combine index lookups in e.g. Redis, MongoDB or Lucene with the core graph engine.

See http://docs.neo4j.org/chunked/snapshot/index.html for docs.

/peter