Which of the following is an example of a relational database management system (RDBMS)?

A relational database management system (RDBMS) is a system whose users view data in tables and can manipulate that data using a relational language like SQL. Both MySQL and PostgreSQL are prominent examples of systems that manage data based on the relational model. MySQL is a widely used open-source RDBMS. PostgreSQL is an advanced open-source object-relational database system (ORDBMS), which extends the relational model with object-oriented features, but it is fundamentally an RDBMS and is categorized as such.

A. MongoDB is a NoSQL database that uses a document-oriented data model, not the relational model of tables, rows, and columns.
D. Redis is an in-memory NoSQL data structure store, often used as a cache or message broker, not a traditional disk-based RDBMS.

1. MySQL 8.0 Reference Manual. (2023). Chapter 1, Section 1.2.1, "What is MySQL?". The documentation states, "MySQL is a relational database management system (RDBMS)..."

2. The PostgreSQL Global Development Group. (2023). PostgreSQL 16 Documentation, Preface. It describes PostgreSQL as "a powerful, open source object-relational database system." An object-relational system is a type of relational system.

3. Ramakrishnan, R., & Gehrke, J. (2003). Database Management Systems (3rd ed.). McGraw-Hill. Chapter 1, Section 1.4, "An Example of a Relational Database," lists Oracle, IBM DB2, Microsoft SQL Server, and open-source systems like MySQL and PostgreSQL as leading RDBMSs.