ViSta: a tool suite for the visualization of behavioral requirements

Abstract

ViSta is a tool suite designed to support the requirements specification phase of reactive systems. It enables the user to prepare and analyze a diagrammatic description of requirements using the statechart notation. ViSta includes a template wizard, a graphical editor and a statechart visualization tool. The template wizard guides the user through the steps necessary for the extraction of relevant information from a textual description of requirements. This information is stored in a database that is used by the statechart visualization tool to automatically generate statechart layouts. The statechart visualization tool offers a framework that combines hierarchical drawing, labeling, and floorplanning techniques. Hence, the automatically produced drawings enjoy several important aesthetic properties: they emphasize the natural hierarchical decomposition of states into substates; they have a low number of edge crossings; they have a good aspect ratio, and require a small area. These aesthetic features are invaluable since they allow the user to shift focus from organizing the mental or physical structure of the requirements document to its analysis.

Introduction

Statecharts are widely used for the requirements specification of reactive systems. This notation captures the requirements attributes that are concerned with the behavioral features of a system, and models these features in terms of a hierarchy of diagrams and states. The usefulness of statecharts depends primarily on their readability, that is the capability of the drawing to convey the meaning quickly and clearly. Several visualization tools for the specification of reactive systems are available in the market (Harel et al., 1990; Peterson, 2001; Telelogic, 2001; O'Donnel et al., 1999; Artisan Software Tools, 2001). Even though these tools are helpful in organizing designers' thoughts, they are mostly sophisticated small scale graphical editors, and therefore are severely inadequate for the modeling of complex reactive systems. Specifically, hand made diagrams quickly become unreadable when the specification complexity and size increase. Therefore computer assistance is of paramount importance for the graphical representation of complex reactive systems.

In this paper we present ViSta, a tool suite for the automatic visualization of statechart layouts. We proceed in two steps: we manually extract behavioral information from a textual description, and store it into interactive templates; then ViSta automatically generates graphs that model statecharts in a hierarchical fashion. The resulting drawings enjoy several properties: they have a low number of arc crossings; they emphasize the natural hierarchical decomposition of states into substates; and they have a good aspect ratio. The automatically produced graphical representation is an effective requirements assessment tool since it allows the specifier to shift focus from organizing the mental or physical structure of the requirements to its analysis. In addition, the interdependence between the textual, template and graphical representations ensures consistency between the different documents and therefore facilitates the verification and validation effort.