The factors we have been discussing have led many in our industry to rethink the idea of a database. Engineers wrestled with the limitations of the relational database and set out to build modern web-scale databases. The term NoSQL was coined to label this category of databases. Originally, the term stood for No SQL but has evolved to mean Not Only SQL. To confuse matters further, some NoSQL databases support a form of the SQL dialect. However, in all cases they are not relational databases.
While the NoSQL landscape continues to expand with more projects and companies getting in the action, there are four basic categories that databases fall into: