please find the below info.
The NetBackup server software collects data from NBSL in the following ways:
Initial data load
Listening for change notifications or events
Whenever NetBackup server software starts, when data collection for a master server is enabled or when a master server is added to NetBackup, the OpsCenter server starts collecting all the available data from NetBackup master server into the OpsCenter database using NBSL. The initial data load happens serially for each data type. As soon as the initial data load is complete, the NetBackup server software listens to the notifications that are sent by NBSL for any change in NetBackup data. Then NetBackup updates the NetBackup database.
It's for more than just OpsCenter. When the NetBackup Console needs data from NetBackup (client configurations, policies, jobs, ...), or to update NetBackup, it goes through NBSL. For example, to show the contents of a backup image in the BAR panel, NBSL performs a bplist command and returns the output to the GUI.