Introduction
Usability of software applications, websites, interfaces, and the ease with which a user is able to complete the tasks by using a website or software application. A website or application that has high usability allows users to easily accomplish the tasks, learn easily, and gives a pleasing experience. Several organizations such as ISO/IEC 9126, ISO 9241, and IEEE Std.610.12 have defined certain standards of usability, and software developers or website designers are expected to follow the standards as defined in these organizations. This paper examines the decomposition aspects of usability.
Decomposition of Usability
The section gives an understanding of Usability as per ISO 9126 and ISO 9124. Decomposition of attributes is also provided.
ISO/IEC 9126-2001
As per ISO/IEC 9126-2001, software quality is governed into six categories and are Portability, Usability, Functionality, Maintainability, Efficiency, and Reliability. Decomposition is based on the view of the users and brings in the aspect of quality. There are four parts to the ISO/ IEC 9126. As per the ISO/9126 standard, usability is defined as “A set of attributes that bear on the effort required for use and on the individual assessment of such use by a stated or implied set of users”. The decomposition of Usability is understandability, learnability, operability, attractiveness, usability, and compliance (Abran, 2002).
ISO 9241-11-98
ISO 9241-11-98 gives the recommendations and the requirements for software, hardware, ergonomics and the user environment and all these factors contribute to define usability. There are 17 parts in this standard: part 1 to 2 deal with the general requirements; parts 3 to 9 provide for the material requirements; part 9 provides for the environment requirements while parts 10 to 17 deal with the software requirements. The standard defines Usability as: “Software is usable when it allows the user to execute his task with effectiveness, efficiency and satisfaction in the context of use specified”. The decomposition are dialogue principles, usability specifications and measures, information presentation, user guidance, menu dialogues, command dialogues, direct manipulation dialogues and form filling dialogues (Abran, 2002).
Comparison of the two standards
The ISO/IEC 9126-2001 standard utilises an approach that is product oriented and usability was not dependant on the quality of the software, how many defects it had, if it crashed and so on. Usability depended mainly on the interface components such as radio buttons, hyperlinks, web safe colours, drop down boxes, text entry boxes and so on and the emphasis was on how easy users felt when using a software.
There was no focus on how well the software actually performed, how efficiently the data tables were created, nesting of tables and so on. But the attributes for a software product means that usability would depend essentially on the type of user, the task that had to be carried out and the environment in which the user worked. While using an approach that is product oriented, the quality of software is not taken into consideration. But ISO/ IEC: 9126-2001 suggests that the capability of the application, website or software has to learned, understood and accepted by the user when the utilised under a set of specified conditions (Abran, 2002).
In ISO 9241, the part 11 sections explains the importance and process and steps to be considered when specifying the attribute of usability as a measure of the satisfaction of users and their performance. The standard uses three quality attributes for understanding the usability and they are: effectiveness, where it is ascertained how the user would complete the tasks that they wanted to achieve when they decided to use the application; efficiency, where the extent of resources that have to be consumed to complete the tasks and Satisfaction where the users would feel satisfaction on using them system.
The ISO 9241 standard has set guidelines that are utilised to evaluate the usability as per the software context but it must be understood that the results that are got from the evaluation depend on the context of the application and the objectives to be achieved for evaluation. Understanding the context and attributes of the use can create usable items and products. Context characteristics include tasks, users and environment and these can be major issues when it is required to determine the usability as a characteristic of the product.
The concept of usability again depends on the expected skill of users and a product that is made for advanced and experienced users may not be apparent to a novice or unskilled user. Features such as the user interface of a system can be made better by using web safe colours that are not jarring to the eye, avoiding use of animated gifs that can induce heart attacks, by proper use of background and skin colours by using menus, fonts and font colours that are easily readable. Some applications give a prompt when a mouse over is done and the popup text gives information that cannot be put on a button (Abran, 2002).
ISO 9241-11-98 has certain advantages over ISO/IEC 9126-2001 and they are: ISO 9241 focuses on aspects of usability and the context of components use has to be considered while evaluating the design, usability and specification evaluation. Satisfaction of the user and the performance can be used to give direct measurements of the extent of usability for a certain context. The measurement of satisfaction and performance of the user gives a base that can be used for comparison between other features of design and usability for a certain context. To a large extent, usability can be defined by the standard to conform to the requirements of ISO 9001 (Abran, 2002).
ISO 9241-11-98 has certain disadvantages over ISO/IEC 9126-2001 and they are: the usability is addressed form the view of the process to be used and hence it becomes a viewpoint process while ISO 9126 is a product viewpoint. ISO 92411 does not consider issues such as the learnability and this is required by different standards. The standard also does not consider the aspects of security and this is regarded as very important when software is to be evaluated for usability (Abran, 2002).
Design of a Questionnaire for Usability
The following questionnaire can be used to evaluate the usability. The SUMI questionnaire is based in the software usability measurement inventory and it s testing method that is used to measure the usability and software quality. There are different subscales in the tool and they are: global, Efficiency, Affect, Helpfulness, Control and Learnability. A commonly used application can be used to assess its usability and users can be asked to fill the questionnaire with a rating point from 1 to 5 on the Liker scale. A score of 1 means totally disagree while 5 would mean fully agree. (SUMI, 2007).
Please refer to the following table.
The above questionnaire has to be submitted to individuals and the score has to be noted and entered as an average for the corresponding scale. The total score divided by the number of users would then give the average of the usability index.
Useful Objective Measures for the future
Bevan (2001) has proposed a new model that would be a better representation of usability. According to this model, Usability could have the following decompositions: Efficiency, Effectiveness, Satisfaction, Security and Learnability. These decompositions would have a number of sub attributes that would cover the gaps in both the ISO models. Effectiveness would have measures such as percentage of tasks accomplished, ration on failure of handling and percentage of tasks achieved per unit of time.
Efficiency would have measurable attributes such as numbers of good and bad characteristics recalled by users, time to achieve one task, time spent on errors, error percentage, documentation of helps use frequency, revisions number of failed commands, number of available commands not called upon. Satisfaction measure would have percentage of users favourable and unfavourable comments. Security would have measures of easy human readiness, ease of executions cancellations by users, easy input and output and instruction readiness. The learnability would have a measure of search time for information.
Conclusion
The paper has examined standards of ISO 9241-11-98 and ISO 9126 and examined various decompositions and sub attributes of each along with a definition of usability as per the two standards. The paper has also discussed the merits and demerits of the two standards and presented a questionnaire that can be used to assess the usability of a site. Future recommendations based on the two standards have also been made.
References
Abran Alain. 2002. Consolidating the ISO Usability Models: Usability measurements for ISO 9241 and ISO 9126. Concordia University, Montreal, Canada.
Bevan N. 2001. A proposed standard for consumer product usability. UAHCI, New Orleans.
SUMI. 2007. Questionnaire based usability testing. Web.