What's the use of this table '/scwm/d_wb_pdi'?

I found that the number of entries ot table '/scwm/d_wb_pdi' is less than table '/SCDL/DB_PROCH_I', some records in table '/SCDL/DB_PROCH_I' but not in '/scwm/d_wb_pdi'. So,what's the use of this table and in what case the data in this table will be updated?