The familiar Neo4j treats relationships as first class citizens; ad hoc queries/ traversals, integrity (if one node is deleted, the link is gone) etc. It also advertises as the only mechanism to denote relations as well as outperform joins of relational DBs.
How powerful are Riak links to denote relationships? Can they be used to answer ad-hoc queries like "fetch a list of hobbies for each such person who earns more than x" or friend of a friend, assuming suitable features like secondary indexes? In general, can they simulate the output of a join in an RDBMS?
Are they also meant for heavy use, such as a social bookmarking system where there are lots of links for a person and bookmarks? Or are they meant for careful use (all structures must be directed acyclic graphs)?
In the "not do" category:
- Link integrity is not enforced
- It cannot answer "what links to this node?"