Data Stream Linkage Mechanism

(DSLM), a program can be built by linking program modules to form a network through which data passes. The network is speciJed by the program designer using a mixture of pre-coded and custom coded modules. This linkage technique and the capabilities that result from it constitute an approach to programming that is radically diferent from conventional techniques. It can increase the productivity of programmers and can result in programs that are easier to understand and to maintain. This paper gives examples based on a specijic implementation of ' DSLM and describes some of the experience gained from the implementation over the last six years. Symptoms of a problem in conventional application development have been evident for a long time. Almost every programmer has experienced cost and schedule overruns, long debugging times, and difficult and costly maintenance of programs. Solutions that have been tried include various clerical and management disciplines and a number of novel programming languages and programming techniques, with varying degrees of success. ' It has been proposed that the problem could be addressed by applying engineering disciplines to application development. " A key concept referred to as design modularity was identified by R. B. Miller of IBM as early as 1966.3 It provided principles on which systems could be designed in terms of modules with well-defined functions. The intent was to allow easier construction of new systems and modification of existing ones. While there are doubtless many reasons for our inability to achieve this modularity in programming, a major factor identified by a number of writers is the control-flow orientation of conventional pr~gramming.~' This orientation is related to the fact that Copyright 1978 by International Business Machines Corporation. Copying is permitted without payment of royalty provided that (1) each reproduction is done without alteration and (2) the Journal reference and IBM copyright notice are included on the first page. The title and abstract may be used without further permission in computer-based and other information-service systems. Permission to republish other excerpts should be obtained from the Editor.