> "MongoDB, Cassandra, Redis, or Hadoop"
Adding Hadoop in the mix tells me he doesn't know what a NoSQL is.
Adding Hadoop in the mix tells me he doesn't know what a NoSQL is.
Of course we can bikeshed all day and split hairs about the precise definitions, but in the spirit of pragmatism, I would absolutely put "Hadoop" as a form of NoSQL storage solution. In fact, I'd say the most distinct of the items mentioned is Redis, and Redis is the tool from this list that has use cases that tend to differ the most significantly from traditional RDBMSs (I'm thinking specifically cases where Redis is used as a buffering layer to help relieve congestion for a highly visited base data store). But even so, I still don't think it represents any sort of taxonomic error to put them all in the NoSQL category, at least for practical purposes.
But now, that Cassandra has SQL like query language, hadoop has SQL like hive and other NoSQLs implement semi-SQL interfaces, I believe a good definition is a database that is not one of
1. ACID
2. Strongly typed table schema.
There really isn't any such thing as SQL/NoSQL any more.
Having a SQL-esque query language is very far from the implications of "doing SQL":
- Any external software that relies on SQL (not a similar language that looks like but it isn't) won't work.
- Any tool which expects SQL and expects SQL-based drivers (like JDBC, for instance) won't neither work.
- SQL is a huge standard with a significant number of features. This semi-SQL interfaces, at best, implement a tiny part of that used to be SQL 92, a standard by the Windows 3.1 era. So not a big deal if you compare with modern SQL implementations in databases like PostgreSQL.
So I think they are still very bound by the definition that they don't do SQL.