What do relational databases allow for in relation to flat-file databases?

Relational databases allow for the combination of flat-file databases linked by key fields, which is a fundamental aspect of their design. In a relational database, data is organized into tables, and these tables can be related to each other through common fields, often referred to as keys. This structure facilitates complex data relationships, enabling users to efficiently retrieve and manipulate data across different tables.

By linking these tables through primary and foreign keys, relational databases help maintain data integrity and reduce redundancy, which are significant limitations found in flat-file databases where data is often duplicated and not organized in a relational manner. This capability to connect multiple tables based on relationships is what distinguishes relational databases from simpler flat-file models, leading to more sophisticated data handling and queries.

While the other options mention aspects like security, management, and data capacity, they do not directly capture the core functionality that differentiates relational databases in terms of their ability to integrate and link multiple datasets effectively.