Open Source NoSQL Databases
For almost a year now, the idea of “NoSQL” has been spreading due to the demand for relational database alternatives. Maybe the biggest motivation behind NoSQL is scalability. Relational databases don’t lend themselves well to the kind of horizontal scalability that’s required for large-scale social networking or cloud applications, and ORMs can abstract away impedance mismatch only so much. In other cases, companies just don’t need as many of the complex features and rigid schemas provided by relational databases. Most people are not suggesting that we all ditch the RDBMS, in fact, many companies don’t really need to switch. Relational databases will probably be necessary for many applications years and years from now. In essence, NoSQL is a movement that aims to reexamine the way we structure data and draw attention to innovation in hopes of finding the solution to the next generation’s data persistence problems.
Check the source for details on various types of NoSQL.