The implementation of an interactive data entry system for Pascal programs

This thesis develops a screen-oriented interface for providing input data to interactive PASCAL programs in VAX/VMS. The inherent problem of processing in a batch mode is that the program aborts when input errors occur at execution time. Screen Pascal is a language extension to ordinary Pascal which has mechanisms for controlling interactive data entry. It performs validity checks on each input item, including type, range and user-specified constraint checks. In case an error is detected, Screen Pascal rejects the value and requests a reentry. Assertions regarding the overall logical and consistency relationships of input data are also considered. These early validity checks ensure that the program continues processing after an erroneous input is detected and corrected. Screen Pascal allows the user to control the screen format and define the field specifications. Many techniques for preventing errors, such as field attributes and CRT features have been employed in the system.