When compared to relational databases, NoSQL databases are more scalable and provide superior performance, and their data model addresses several issues that the relational model is not designed to address when dealing with large volumes of structured, semi-structured, and unstructured data.
To achieve this, requires a wide variety of different database designs developed in response to a rise in the volume of data stored, the frequency in which this data is accessed, and performance and processing needs.
Types of NoSQL databases can be (roughly) classified under the following four headings:
Key-value stores: These are among the simplest NoSQL databases. Every single item in the database is stored as an attribute name (or "key"), together with its value.
Document databases: These pair each key with a complex data structure known as a document, which themselves may can contain many different key-value pairs or key-array pairs, or even nested documents.
Wide-column stores: These...
