1. OVRDBF is basically use to teporarily change the attributes of file,
we can do reflect of that changes in attributes on either Joblevel, Call level and Activation Group level which is defined in OVRDBF.

2. If we want to set the pointer of any file either on RRN,Key values for that we can also used it.

Eg. If suppose at the time of compiling the Database file,the attributer Share was set to *NO, and now i want to do it in my PGM as SHARE(*YES) then i will use OVRDBF.

Hope you find your answer, let me know for any further confusion/clarification.