Supporting concurrency, communication, and synchronization in human-computer interaction—the Sassafras UIMS

Abstract

Sassafras is a prototype User Interface Management System (UIMS) specifically designed to support a wide range of user interface styles. In particular, it supports the implementation of user interfaces where the user is free to manipulate multiple input devices and perform several (possibly related) tasks concurrently. These interfaces can be compactly represented and efficiently implemented without violating any of the rules of well-structured programming. Sassafras also supports elaborate run-time communication and synchronization among the modules that make up the user interface. This is needed to implement user interfaces that have context-sensitive defaults, and it simplifies recovery from semantic errors. Sassafras is based on a new language for specifying the syntax of human-computer dialogues known as Event-Response Language (ERL) and a new run-time structure and communication mechanism for UIMSs known as the Local Event Broadcast Method (LEBM). Both ERL and LEBM are described in detail, and implementation techniques are presented. The effectiveness of Sassafras is demonstrated by describing two interfaces that have been implemented with Sassafras.