Document-format databases store data in what format?

Document-format databases are designed to store data in a flexible, semi-structured format, which typically takes the form of nested key-value pairs. This structure allows each document to contain different fields and data types, making it suitable for a wide variety of data applications. The nested key-value model enables complex data structures to be stored, such as arrays and embedded documents, which is particularly useful for representing hierarchical data.

In contrast, flat files are generally simple, one-dimensional structures without the capability to represent nested relationships. Excel-like structures tend to organize data in rows and columns, which do not accommodate the flexibility found in document databases. SQL tables follow a strict schema with defined columns and data types, which contrasts sharply with the inherent flexibility of document-format databases that can handle varying structures within the same database.

This unique capability of handling various data structures within a single document is what makes the nested key-value pairs the defining characteristic of document-format databases.