what is distinction between NoSql DB and OO Db?
An item-oriented database, like db4o, could be one among the options presented by NoSQL, meaning Not Just SQL. It's some options to relational databases: Voldemort, Hadoop, MongoDB, CouchDB, BigTable, Neo4J, db4o yet others.
NoSQL is really a movement, OODB is really a technology. Or quite simply: NoSQL is someone, an OODB is a bit of code.
There is no strict meaning of "NoSQL", therefore the variations are largely semantic. Generally an item Oriented Database is recognized as a subset (a type of) NoSQL Database. However, generally an OO DB will have Acidity-like securing to help keep consistency, while NoSQL will normally possess some type of "eventually consistent" or partial securing semantics. A NoSQL's schema might be object-based or might be key-value based (or something like that else), which makes it a far more general term.