NoSQL is a term generally used to describe any database management system that uses a non-relational data model. The following table lists several NoSQL data models and highlights a few of the popular open-source databases that implement them, but please note that this is not a comprehensive list:
|Operational Database Model||Example DBMSs|
|Key-value store||Redis, MemcacheDB|
|Columnar database||Cassandra, Apache HBase|
|Document store||MongoDB, Couchbase, Elasticsearch|
|Graph database||OrientDB, Neo4j|
These different data models can allow for far greater flexibility than the rigid structure imposed by relational databases. Because of their flexibility, NoSQL databases have a reputation for being a better choice for storing semi-structured and unstructured data, as opposed to the normalized, structured data required by relational databases. Since NoSQL databases don’t come with a predefined schema, it’s typically up to developers or database administrators to define how the data should be organized and accessed in whatever way makes the most sense for their application.
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A complete list of our educational resources on NoSQL can be found on our NoSQL tag page.