I recently added a fairly feature rich Graph Database to AlchemyDB (called it LuaGraphDB) and it took roughly 10 days to prototype. I implemented the graph traversal logic in Lua (embedded in AlchemyDB) and used AlchemyDB's RDBMS to index the data. The API for the GraphDB is modeled after the very advanced GraphDB Neo4j. Another recently added functionality in AlchemyDB, a column type that stores a Lua Table (called it LuaTable), led me to mix Lua-function-call-syntax into every part of SQL I could fit it into (effectively tacking on Document-Store functionality to AlchemyDB). Being able to call lua functions from any place in SQL and being able to call lua functions (that can call into the data-store) directly from the client, made building a GraphDB on top of AlchemyDB possible as a library, i.e. it didn't require any new core functionality.
via NoSQL databases