Informix and DB2 are examples of what type of databases?

Informix and DB2 are indeed examples of proprietary relational databases. These databases are specifically developed and owned by their respective companies, which means that access to the software, support, and specific features is typically controlled through licenses. Unlike open-source databases, which allow users to modify and distribute the software freely, proprietary databases come with licensing fees, restrictions on their use, and support that is typically provided directly by the vendor.

Relational databases like Informix and DB2 store data in structured formats using tables, where relationships between the data elements are well defined. This structured approach enables complex querying and data integrity through the use of primary and foreign keys. The proprietary nature of these products often comes with advanced features, robust performance, technical support, and additional tools that are tailored to organizational needs, which can be essential for enterprise-level applications and critical data management.

The other options do not describe Informix and DB2 accurately. Open source relational databases, for instance, are those which allow for public access and modification, while distributed databases refer to systems that store data across multiple locations. NoSQL databases are designed for unstructured data and are fundamentally different in their approach to data management compared to relational databases.