Who or what is responsible for maintaining database consistency?

The RDBMS (Relational Database Management System) is responsible for the control of the database however it requires appropriate planning and implementation of your design in order for this to work properly. Further proper maintenance of the Database environment is critical to its on-going operation. In short proper design by the database architect followed by proper implementation of this design by the DBA or SQL Developer coupled with proper SQL environment deployment is responsible for the healthy operation of a RDBMS.