The most abstract design rules are general principles, which can be applied to the design of an interactive system in order to promote its usability. Principles can provide the repeatability which paradigms in themselves cannot provide.
In this article, we present a collection of usability principles that we can use for interactive systems.
The principles we present are first divided into three main categories:
In the following, we will subdivide these main categories into more specific principles that support them. Let’s look at those principles in brief.
⚫ Principles of Learnability
Learnability concerns about novice users to understand how to use it and how to attain a maximum level of performance.
In the following, I mention a brief introduction of specific sub-principles that support learnability.
1) Predictability supports for the user to determine the effect of future action based on past interaction history.
2) Familiarity is the extent to which a user’s knowledge and experience in other real-world or computer-based domains can be applied when interacting with a new system.
3) Synthesizability supports the user to assess the effect of past operations on the current state.
i. Principle honesty : after moving to its new location in the file system, able to determine its new whereabouts.
ii. Command line — have to remember the destination path then ask to see the contents to verify
iii. Visual Interfaces — visual representation of the file is dragged from its original directory and placed in its destination directory where it remains
4) Generalizability supports for the user to extend knowledge of specific interaction within and across applications to other similar situations.
5) Consistency is the likeness in input-output behavior arising from similar situations or similar task objectives.
⚫Principles of Flexibility
Flexibility means the multiplicity of ways in which the end-user and the system exchange the information.
1) Multi-threading is the ability of the system to support user interaction about more than one task at a time.
2) Task migratability is the ability to pass a control for the execution of a given task so that it becomes either internalized by the user or the system or shared between them
3) Dialog initiative is allowing the user freedom from artificial constraints on the input dialog imposed by the system.
4) Substitutivity is allowing equivalent values of input and output to be arbitrarily substituted for each other.
5) Customizability is the modifiability of the user interface by the user or the system.
⚫Principles of Robustness
Robustness is the level of support provided to the user in determining achievement and assessment of goals.
1)Observability is the ability of the user to evaluate the internal state of the system from its perceivable representation.
i. Browsability — Allow user to explore the current internal state of the system via limited view provided at the interface.
ii. Defaults — Assist the user by passive recall. Reduces the physical actions necessary to input values.
iii. Reachability — Possibility to navigation through the observable system states. Deals with recoverability
iv. Persistence — Deals with the duration of the effect of a communication act and ability of the user to make use of it. Email notification. Persistent visual representation
v. operation visibility
2) Recoverability is the ability of the user to take corrective action once an error has been recognized.
3) Responsiveness is how the user perceives the rate of communication with the system.
4) Task conformance is the degree to which the system services support all of the tasks the user wishes to perform and in the way that the user understands them.
⚫Standards and Guideline for Interactive systems
Standards set by national or international bodies to ensure compliance by a large community of designers standards require sound underlying theory and slowly changing technology. Hardware standards more common than software with high authority and low level of detail. ISO 9241 defines usability as effectiveness, efficiency, and satisfaction with which users accomplish tasks
Guidelines are more suggestive and general. many textbooks and reports full of guidelines.Understanding justification for guidelines aids in resolving conflicts.
Abstract guidelines (principles) applicable during early life cycle activities
Detailed guidelines (style guides) applicable during later life cycle activities
⚫Shneiderman's 8 Golden Rules
This set of rules gives a summary of the key principles used in interface designing.
Rules in brief:
- Strive for consistency
- Enable frequent users to use shortcuts
- Offer informative feedback
- Design dialogs to yield closure
- Offer error prevention and simple error handling
- Permit easy reversal of actions
- Support internal locus of control
- Reduce short-term memory load
⚫Norman’s 7 Principle
Norman’s seven principles also provide a summary of user-centered design philosophy.
Principles in brief:
- Use both, knowledge in the world and knowledge in the head.
- Simplify the structure of tasks.
- Make things visible: bridge the gulfs of Execution and Evaluation.
- Get the mappings right.
- Exploit the power of constraints, both natural and artificial.
- Design for error.
- When all else fails, standardize.
My next article is about another sub-topic in human-computer interaction. It is “Evaluation techniques for interactive systems”.