COBOL BL

 DMAP compiler option create the data division map in the compile listing. BL, base locator, etc just the base address for a 4K block of virtual memory. BL is an index (start from 1) to a table of base address kept in TGT (target global table). The value is to be loaded into a GPR as base register. A field in data division can be access with a displacement. The compile listing will show the BL and DISP clay for each field in the program. 

BLL (base link locater) is similar to BL but for field defined in the linkage section of the program. BLL actual storage valus are also kept in TGT