document stores

Document stores, also called document-oriented database systems, are characterized by their schema-free organization of data.

That means:

Records do not need to have a uniform structure, i.e. different records may have different columns.
The types of the values of individual columns can be different for each record.
Columns can have more than one value (arrays).
Records can have a nested structure.

Document stores often use internal notations, which can be processed directly in applications, mostly JSON. JSON documents of course can also be stored as pure text in key-value stores or relational database systems. That would, however, require client-side processing of the structures, which has the disadvantage that the features offered by document stores (such as secondary indexes) are not available.

Document Stores

Most popular examples