DPL: A Language for Instruction in CONTEMPORARY DATA PROCESSING CONCEPTS
Morgan, Howard L.
The Data Processing Language (DPL) id designed with two aims. The first is to aid in teaching the concepts and techniques of contemporary data processing systems to those who need an appreciation of the field, but who do not need to become trined programmers. The second is to test a new method for organizing and programming large systems which share a common data base among several simultaneous users. The criteria for a contemporary data processing language are set forth and DPL is shown to meet them. These include remote terminal management, handling of shared data bases, file and device oriented input and output, and standard arithmetic and text processing features. In addition, simple syntax and extensive error detection and correction features fulfill important requirements of instructional computing systems. Interrupts are the basis for the new method of systems organization. The DPL programmer can specify conditions when interrupts should be generated, e.g., when the relation $X+Y=34$ is true, and can specify the routine which should be called to process each interrupt. The DPL monitoring system detects the occurrence of these conditions and generates the interrupts. Some of these variables involved in conditions which can generate interrupts may be in files. The programmer can attach to those files the interrupt processing routines and the interrupt conditions. When the file is read in, the system begins monitoring these attached interrupt conditions and may execute the attached interrupt processing routines, which are called file tags, even though the user who placed the tags on the file is no longer in control. Several interrupts may be generated as the result of the execution of a single DPL statement, and interrupts may be generated while executing an interrupt processing routine. Therefore, an algorithm is presented which schedules the execution of the interrupt processing routines. A management information system may thus be composed of two parts: a data base of tagged files, and a supervisor program which handless interaction with remote terminals and performs background tasks. This new organization is shown to have value both for its instructional clarity and for designing and programming large integrated information systems.
computer science; technical report
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