What is a characteristic of the Object-Relational DBMS?

The characteristic of an Object-Relational Database Management System (DBMS) that makes it unique is its ability to combine relational and object-oriented features. This integration allows for a more versatile approach to data handling, enabling the use of complex data types and structures such as objects, classes, and inheritance while still maintaining the traditional relational model's capabilities.

By blending these two paradigms, Object-Relational DBMS can store complex data in a way that is not possible with purely relational systems, which typically manage data in flat table structures without the object-oriented features. This combination enhances the modeling power of a database, allowing it to handle intricate data relationships and behaviors that align with real-world entities more effectively.

In contrast, a DBMS that only supports flat table structures lacks this advanced functionality, and those based solely on hierarchical data structures do not incorporate the flexibility of object-oriented principles. Additionally, the notion that it does not allow structured data is inaccurate, as Object-Relational DBMS are specifically designed to handle structured data efficiently along with more complex types.