Mainframe Programming: COBOL, CICS, and REXX

Map generation produces two outputs: the map copybook (containing data structure definitions for the map) and the load module (the executable runtime version). These outputs are used respectively for compilation reference and actual execution in mainframe environments.

To enable extended attributes (such as color, highlighting, and validation) in CICS BMS maps, you must specify EXTATT=YES (or EXTATT=MAPONLY/YES) in the DFHMSD macro definition along with the appropriate terminal type.

BMS (Basic Mapping Support) map sets are registered in the Program Processing Table (PPT), which defines the programs and mapsets available to CICS. The PPT contains entries for all transaction programs and associated mapsets, making it the correct table for BMS map registration. RPT is for resource definitions, PCT for program processing transactions, and LCT doesn't apply to BMS maps.

CICS stands for Customer Information Control System, which is IBM's transaction processing subsystem for mainframe systems. It manages online transaction processing and provides communication between the terminal and application programs. The key phrase 'Customer Information' is what CICS represents.

In CICS BMS, the physical map is the compiled load module that contains screen formatting data and is loaded at runtime. The symbolic map is a copybook data structure that your program uses to interact with the map fields. This separation allows the program to work with named fields while CICS handles the actual screen layout.

In CICS BMS, every field on a map uses three working storage fields: Length (the field length), Attribute (field attributes like protection/visibility), and Input/Output (the actual data field). These three components allow programs to properly interact with screen fields, handling both display and data input.

In COBOL, the REDEFINES clause allows a field to redefine another field's storage, but the redefining field cannot be larger than the original field. X(100) defines an alphanumeric field of 100 bytes, which cannot be redefined with X(200) (200 bytes) as this would exceed the allocated storage space. The redefining field must be the same size or smaller.

In packed decimal (COMP-3) format, each byte contains two decimal digits, except for the last byte. The last byte contains one digit in its first half (nibble) and the sign representation (such as C, D, or F in hex) in its last nibble.

COMP-3 (packed decimal) format stores each digit in 1/2 byte (nibble). For S9(7), we have 7 digits plus 1/2 byte for the sign, totaling 8 half-bytes = 4 bytes. The formula is (number of digits + 1) / 2 bytes.

All statements are true. A subscript represents the occurrence number, while an index represents the displacement. An index can only be modified using PERFORM, SEARCH, and SET. An index is required on a table to use SEARCH or SEARCH ALL. Thus, none of the statements are false.

The INITIALIZE verb in COBOL sets alphabetic, alphanumeric fields, and alphanumeric edited items to spaces. Numeric and numeric edited items are set to zero. FILLER and OCCURS DEPENDING ON items remain unchanged.

Level 66 is specifically used for the RENAMES clause in COBOL. It allows you to regroup existing data elements by giving a new name to a contiguous set of elementary items. Level 88 is for condition names, and level 77 is for independent elementary items.

In COBOL, ORGANISATION IS SEQUENTIAL with RECORDING MODE F (Fixed) and BLOCK CONTAINS 0 defines a Fixed Block file. This means records are fixed-length and blocked together for efficient I/O.

The Data Division in a COBOL program can contain up to six sections: File Section, Working-Storage Section, Local-Storage Section, Linkage Section, Communication Section, and Report Section.

In COBOL, all three file organizations (INDEXED, RELATIVE, and SEQUENTIAL) support all four open modes: INPUT (read-only), I-O (read/write), OUTPUT (write-new), and EXTEND (append).

In COBOL (specifically COBOL 85 and later standards), the maximum number of nested OCCURS clauses (subscripts/indexes) allowed is 7. Older standards like COBOL 74 limited this to 3.

In COBOL file status codes, 35 indicates an 'Empty File' condition when attempting to read from a file that exists but contains no records. This is a standard file status code used in COBOL file operations. Code 10 typically indicates end-of-file, while other codes represent different error conditions.

In REXX, when a subroutine completes execution and returns a value using the RETURN instruction, that value is automatically stored in the special variable named RESULT.

In TSO/E REXX, EXECIO is the primary command used to perform input and output operations, such as reading from or writing to sequential datasets or partitioned data set members.

In REXX, the DATA STACK can be used for file I/O operations - you can PUSH lines to write to a file and PULL/QUEUE to read from a file. QUEUE is used for stack manipulation but not direct file I/O. COMPOUND and SYMBOLIC variables are data types, not I/O mechanisms.