Everybody knows that dealing with hierarchies in a relational database is awkward, and depending on your needs it gets ugly, or downright impossible to do quickly in SQL (lots of queries needed, etc).
- you could do such operations with simple single queries?
- you could have not only simple trees but also complex ones (multiple parents) ?
- you could have complex graphs for friend-of-a-friend or other structures?
GRAPH engine does all that, without breaking a sweat. Externally it looks like a table and a storage engine, but internally it's a computational engine, in this case specialised for graph operations.