Source : Free On-Line Dictionary of Computing

Rdb
     
        {Oracle Rdb}

rdb
     
        A roll-your-own {database}, created in the {Unix} toolkit
        philosophy.  It appears to be written in the {awk} language,
        and is very compatible with awk.  It uses awk's syntax and can
        be combined with awk commands.
     
        The definitive introduction is "Unix Relational Database
        Management: Application Development in the Unix Environment",
        by Rod Manis, Evan Schaeffer, and Robert Jorgensen, published
        by Prentice Hall.  The book tells how to use rdb to create
        database/spreadsheets in the awk tradition, only easier. It's
        a good way to get into programming for novices.  It's also a
        good way to learn DB theory and construction quite painlessly.