Interactive System Usability (Human-Computer Interaction)

Human-Computer Interaction (HCI) definition according to ACM SIGCHI  is the discipline related to the design, evaluation, and implementation of interactive computer systems for use by humans and studies of the phenomena associated with it.

According to the ISO/IEC 9126 "The usability is a set of attributes that bear on the effort needed for use, and on the individual assessment of such use, by a stated or implied set of users which are Understandability, Learn Ability, Operability, Attractiveness"

The usability goals based on ISO 9241 -  focus on effectiveness, efficiency, and satisfaction.

Usability measures 5 human factors central to community evaluation :

1. Time to learn
2. Speed of performance
3. Rate of errors by users
4. Retention over time
5. Subjective satisfaction

Motivations of usability 

The motivation of usability is because many interfaces are poorly designed and this is true across domains such as below explained with the reasons :

- Life-Critical ( System Air traffic control, nuclear reactors, power utilities, police & fire dispatch systems, medical equipment) which cost High, the reliability and effectiveness are expected. Length training periods are acceptable despite the financial cost to provide error-free performance and avoid the low frequency but high cost errors Subject satisfaction is less an issue due to well motivated users.

- Industrial and commercial systems ( Banking, insurance, order entry, inventory management, reservation, billing, and point-of-sales systems). Ease of learning is important to reduce training costs. Speed and error rates are relative to cost. Speed of performance is important because of the number of transactions.Subjective satisfaction is fairly important to limit operator burnout 

- Office Home and Entertainment Applications ( Word processing, electronic mail, computer conferencing, and video game systems, educational packages, search engines, mobile device, etc.). Ease of learning, low error rates, and subjective satisfaction are paramount due to use is often discretionary and competition fierce. Infrequent use of some applications means interfaces must be intuitive and easy to use online help is important

- Exploratory, Creative, and Cooperative System ( Web browsing, search engines, artist toolkits, architectural design, software development, music composition, and scientific modeling systems ). Collaborative work. Benchmarks are hard to describe for exploratory tasks and device users. With these applications, the computer should be transparent so that the user can be absorbed in their task 

- Social - technical System ( Complex systems that involve many people over long time periods ). Voting, health support, identity verification, crime reporting. Trust, privacy, responsibility, and security are issues. Verifiable sources and status feedback are important. Ease of learning for novices and feedback to build trust. Administrators need tools to detect unusual patterns of usage

Universal Usability

Diversity of human abilities, backgrounds, motivations, personalities, cultures, and work styles is a challange for interface designers. Understanding of differences between users is vital for participation by broadest set of users. Mobile device use has begun to require for designs that are universal usable

Rethinking interface designs for different situations often results in a better product for all users. The rethinking covers considerations for users with disabilities, older adults, young users, etc and discussion for hardware and software diversity