Answer
The sde schema's db_ev_alter_st_metadata, db_ev_drop_st_metadata, and db_ev_rename_metadata triggers are database event triggers used to maintain the st_geometry metadata tables when tables containing st_geometry attributes are altered, dropped, or renamed.
The db_ev_alter_st_metadata trigger is executed after every ALTER TABLE command in the database. The trigger first checks if the table being altered is registered as an st_geometry table, and if it is, updates the metadata accordingly based upon the event.
The db_ev_drop_st_metadata trigger is executed after every DROP TABLE command in the database. The trigger checks if the table being dropped contains an st_geometry attribute; if yes, the trigger removes the metadata from the st_geometry_columns and st_geometry_index tables.
The db_ev_rename_st_metadata trigger is executed after every RENAME command in the database. The trigger checks if the table being renamed contains an st_geometry attribute; if yes, the trigger updates the metadata to reflect the new name of the table.
These triggers should never be modified or removed from the sde schema or the st_geometry metadata will not be correctly maintained as schema changes occur in the Oracle instance.