1.10. Quality and Usability
Usability is the ability of the software to help the users achieve their goals [Constantine and Lockwood 1997]. This is an important issue to be considered in any discussion on software usability. For example, usable software may be very easy to use and may have all the “bells and whistles” features, but if that software is not able to satisfy a particular user requirement then the usability of the software does not add value to the software quality.
Hudson, in listing the top ten user-centered techniques (and correlating them to the ISO13407 human-centered design standard), has put the actual creation of GUI design as the last—the other nine include user analysis, low-fidelity prototyping, navigation design, and scenarios of use. These techniques enable creation of usable software that helps the user achieve her goals in the easiest and simplest possible way. However, since the goals of the user can change, it is essential for usable software to “grow”along with the growing requirements of the user and her growing knowledge and expertise of the software.
1.10.1. Principles of Usability
Constantine and Lockwood [1997] and Constantine [1993] describe the laws of usability followed by the seven principles. The great law of usability states, “The system should be usable by a user with knowledge and experience in the application domain but no experience with the system—without help or instruction.” This law indicates that it is important for the software system to be “instinctively” usable. However, this law does not tell us about the training needs of the users in their application domain. It is up to a good user to know his application domain, and the usability of the software should not be blamed for any lack of application knowledge.
Figure 1.15. Quality and usability
The lesser law of usability states “the system should not interfere with or impede efficient use by a skilled user having substantial experience with the system.” This law recognizes the need for the system to “grow” with the user. For example, I need all the help and tool tips when I use the system for the first time. Later on, as I grow in expertise, this additional help may become more of a hindrance. Usable software recognizes this and enables expert users to use the system without providing unnecessary help.
The principles of usability stated by Constantine and Lockwood include support, structure, simplicity, visibility, reusability, feedback, and tolerance. Each of these principles provides a comprehensive quality angle to the software being designed and produced.
1.10.2. Navigability of Interfaces
In most graphical environments, it is essential for the screens and forms to be organized in a logical and cohesive manner, depending on the needs of the users. For example, a senior insurance broker logging on to a system will usually look for control totals on the insurance risks and premiums accrued, rather than calculate the amount for a particular claim. Similarly, an employee going to an employee portal within the organization and looking for her outstanding annual leave may then want to navigate to her salary and tax screens, rather than the outstanding policy applications. These are some fine nuances in designing the navigation of screens and related interfaces. This navigation becomes all the more important in an Internet-based application, where the logical grouping, dependency, and performance of Web pages are vital for the usability of the application.
1.10.3. GUI Design and Quality
While the user interface is considered separately in any discussion on the software usability, it still remains an important factor in improving the software usability. An interesting discussion on the user interface aspect of usability occurs in Object Modeling and User Interface Design: Designing Interactive Systems, by Mark Van Harmelen [2001].