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How is addressability achieved to the data outside programs working storage?
CICS Interview Questions
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How is addressability achieved to the data outside programs working storage?
The Base Locator for Linkage (BLL) is an addressing convention used to address storage outside the Working Storage Section of an application program. If BLL is used for the input commands (e.g.: READ, RECEIVE), it will improve the performance, since the program would be accessing directly the input buffer outside of the program. In order to work as intended, the program must construct BLL based on the following convention:
1. The parameter list must be defined by means of a 01 level data definition in the Linkage Section as the first area definition to the Linkage Section, unless a communication area is being passed to the program, in which case DFHCOMMAREA must be defined first. The parameter list consists of a group of the address pointers, each of which is defined as the full word binary field ( S9(8) COMP). This is called the BLL cells.
2. The parameter list is following by a group of 01 level data definitions, which would be the actual data areas. The first address pointer of the parameter list is set up by CICS for addressing the parameter list itself. From the second address pointer onward, there is a one-to-one correspondence between the address pointer of the parameter list and 01 level data definitions.
3. VS COBOL II provides CICS application programs with a significant improvements in the area of addressability through the specifial ADDRESS register. Therefore, if an application program is written in VS COBOL II, the program is no longer requires building the BLL cells in the LINKAGE Section.
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