Principles of usability in HCI(Human Computer Interaction)

HCI(Human Computer Interaction) and Usability are becoming core concepts of the system development process to improve and enhance system facilities and to satisfy user needs and necessities.

• HCI assists designers and analysts to identify the needs of texts, fonts, layout, graphics, color, etc. 
• While Usability ensures system the system is efficient, effective, safe, easy to learn, easy to remember, easy to evaluate, and provides job satisfaction to users. 
• ISO 9421 defines usability as effectiveness, efficiency, and satisfaction with which users accomplish tasks.

Principles of Usability:

• Learnability: The ease with which new users can begin effective interaction and achieve maximal performance
• Flexibility: The multiplicity of ways the user and system exchange information
• Robustness: The level of support provided to the user in determining achievement and assessment of goal-directed behavior

1. Principles of Learnability:

• Predictability: It determines the effects of future action based on past interaction history.
• Synthesizability: It determines the effects of past operations on current states. eg.- move file 
• Familiarity: New users can get familiar with the functionality and interaction style of the application.
• Consistency: It means through the resultant behavior of the system. Every time system gives the same result on the same set of inputs.
• Generalizability: It requires specific knowledge of the same domain knowledge. eg.- Cut, Copy, etc.

2. Principles of Flexibility:

• Dialog initiative: All the dialogs are done by a simple request and response system.
• Multithreading: Single set of code on input can be used by several processes at different stages of execution.
• Task Migratability: Transfer the execution of the task from the system to the user and decide who is better. eg.- Spell Checker
• Substitutivity: It allows equivalent values of input and output to be substituted with each other. eg.- Percentages and Grades
• Customizability: It supports the modifiability of the user interface by a user (adaptability) or system (adaptivity).

3. Principles of Robustness:

• Observability: The user should be able to evaluate the internal features of a system and give proper feedback.
• Responsiveness: Real system feedbacks on the user's action.
• Recoverability: To fix and solve errors and get the correct actions.
• Task Conformance: The system supports all the requirements of the user and how the user interacts with them.