![]() ![]() This had the advantage that inclusion of teleprocessing code did not introduce mixed languages in the source: COBOL remained COBOL, PL = I was still PL = I, and Assembler remained Assembler, which made it compliant with all tool support available for these languages. Originally, the user programs requested the services provided by the teleprocessing monitor by means of CALL commands. The screen services are the old solution to customiz- ing the user interface. The screen handling facility displays the maps which are speciÿed with an Assembler-type macro language, extracts the variable ÿeld contents, creates an input data stream from these contents, inserts the variable ÿeld contents from the output data stream and manipulates the appearance of the map based on the attributes of the ÿelds. IMS-DC uses Map Format Service (MFS) and CICS o ers Basic Mapping Support (BMS). Besides this, teleprocessing monitors have their own interface between application programs and terminal devices. Only the system calls are of a higher level since they also provide security checking, logging and error recovery and such. In e ect, the teleprocessing monitor is an operating system within an operating system. It takes care of the control for concurrently running user application programs serving many on-line users. ![]() It establishes the connection to a user terminal, queues the user messages, allocates memory space, copies the next user message into the program input bu er, picks up the output messages from the program output bu er, processes ÿle or database accesses, takes the user program in and out of a waiting state, in- tercepts all service requests by the programs, handles error exceptions, and establishes connections between programs. It provides most of the standard functions required by application programs for communication with remote and local terminals and subsystems. The teleprocessing monitor is itself a complex program which fulÿlls all of the necessary functions required to run a user program in on-line mode. ![]()
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