NoSQL databases are the rage now, aren’t they? Not too long ago, NEJUG hosted a presentation by Tim Berglund called "NoSQL Smackdown." Before giving his tour of several NoSQL databases, Tim tried to give his definition of "NoSQL." After showing the difficulties of defining NoSQL as a series of negatives (no SQL, no relations, no transactions), he merely settled on a vague definition. Basically, he says, NoSQL is merely a set of different approaches in data models, querying and scaling that trade off things like performance and the 3 guarantees of the CAP Theorem.
In other words, there is no such thing as a canonical NoSQL database. Most emphasize key/value or document-oriented storage, but then you have something totally different like Neo4j, a graph database. NoSQL fans like to emphasize scalability, but some candidates don’t really scale. You can’t even say that NoSQL means no SQL, because you have something like GemFire, which does allow you to use SQL. Nevertheless, allow me to give you my own definition of NoSQL. Ready? Here goes:
NoSQL databases are databases for people who don't care about data.