Which of the following is NOT a true relational database?

The identification of Access as a non-true relational database is based on its structure and functionalities when compared to the other options listed. Microsoft Access is primarily classified as a desktop database application designed for small-scale data management. While it does utilize a relational model and can manage relationships between tables, it is often viewed as less mature and robust than the traditional true relational databases utilized in enterprise environments.

In a true relational database management system (RDBMS), such as SQL Server, Oracle, and PostgreSQL, you typically find advanced features and capabilities that support extensive data handling, scalability, security, and multi-user environments that Access may not effectively provide. These systems are designed for larger applications, offering features such as complex transactions, advanced querying capabilities through SQL, and support for large volumes of data and users.

Therefore, while Access does exhibit some relational database characteristics, it primarily serves as a simplified tool for individual users or small teams, making it less representative of true RDBMS systems when evaluated against the capabilities of SQL Server, Oracle, and PostgreSQL.