CAL software design for transferability

Abstract

The successful transfer of CAL software is often thwarted by differences between the computer system on which the software was developed and that on which it is required to be implemented. Facilities which CAL programs may exploit are usually those most vulnerable to change between different computer systems. Drawing upon experience gained in the design, programming, and subsequent transfer of CAL programs in engineering, examples are given of features which may cause problems during implementation and alternatives or improvements are suggested. FORTRAN and GINO-F are proposed as machine and device independent standards, for implementation language and graphics subroutine library, respectively. Good programming practices are described with a view to obtaining readable and easily maintained programs of a sound quality. Importance is placed on modularity in design as the key to writing transportable programs. The idea that every module should conceal some design decisions from all other modules is described with reference to modules that have proved to be particularly useful or advisable. This technique enables a design to be produced in which machine dependencies and difficult design decisions may be confined to a handful of routines. This makes the program more adaptable and gives the teacher and programmer greater freedom to change the implementation, allowing the program to move to any computer system where similar functions can be implemented.