Developing usable web interfaces with the aid of automatic verification of their formal specification

摘要

The development of interactive visual applications is a complex work, usually performed with the help of advanced visual programming environments. Although a number of tools are available to support designers and developers in the specification of a GUI's layout and behavior, and in the generation of the corresponding code that implements the interface, theoretical guidelines and/or semi-automatic mechanisms rely upon the knowledge of the designer to manage usability and accessibility issues. Indeed, the evaluation of the visual environments is traditionally performed by means of expert-based evaluations or by testing with end users. In this work we describe a methodology to specify and evaluate interactive visual environments, in particular web interfaces, based on the SR-Action Grammars formalism and we present a bottom - up approach to aid the designer to develop graphical applications that automatically respect a significant number of usability rules before the software is released and tested by standard methods. We show how it is possible to assess the usability metrics of consistency, completeness and user control by means of checks performed at a high level of abstraction. VALUTA (Automatic Tool for the Usability Verification at Abstract Level) is the implemented tool that allows developers to generate the formal specifica tion of an interactive visual application in automatic manner, so to perform the related usability controls at a very early stage. Thanks to usability controls automatically performed at formal level, the designer can use the evaluation results to perform feedback analysis of the visual environment. The tool is applicable to an already existing interface, allowing the designer to evaluate its usability in the development of a more usable version. We have analyzed the home page of three web sites (www.lycos.it, www.google.it, http://it.mail.yahoo.com/) as a case study and we show the related evaluation report generated by the described approach.