[3] It originally provided a proprietary query interface known as the Relational Data Operator (RDO), but later gained support for ANSI SQL.

[11] Interactive access to the Oracle Rdb can be by SQL (Structured Query Language), RDO (Relational Database Operator), or both.

On OpenVMS systems, Oracle Rdb is a popular (although expensive) upgrade path for applications written using Record Management Services (RMS) files.

Rdb is built on top of a low-level database kernel named KODA, which handles functionality such as locking, journaling, and buffering of data.

[16] Digital provided a relational database for their Ultrix operating system named ULTRIX/SQL, but it was based on Ingres instead of Rdb.