Module 4: Design Rules

Midterm

Design Rules

Rules a designer can follow in order to increase the usability of the eventual software product

Authority

An indication whether or not the rule must be followed in design or whether it is only suggested

Generality

Whether the rule can be applied to many design situations or whether it is focused on a more limited application situation

Principles

(Different Types of design rules)
Are abstract design rules, with high generality and low authority.

• Knowledge of the psych, computational, and sociological aspects of the problem domains and are largely independent of the technology

Standards

(Different Types of design rules)
Are specific design rules, high in authority and limited in application

• It carries a much higher level of authority, it is more important that the theory underlying them be correct or sound

Guidelines

(Different Types of design rules)
Tend to be lower in authority and more general in application

• It is less abstract and often more technology oriented, but they are also general, it is important for a designer to know what theoretical evidence there is to support them.

Learnability

(Principles to Support Usability)
The ease with which new users can begin effective interaction and achieve maximal performance.

Flexibility

(Principles to Support Usability)
The multiplicity of ways the user and system exchange information

Robustness

(Principles to Support Usability)

The level of support provided the user in determining successful achievement and assessment of goal-directed behaviour.

Predictability

(Learnability Principles)
Support for the user to determine the affect of future action based on past interaction history

“Operation Visibility”

Synthesizability

(Learnability Principles)
Support for the user to assess the affect of past operations on the current state

“Immediate/Eventual honesty”

Familiarity

(Learnability Principles)
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.
“Guessability, affordance”

Generalizability

(Learnability Principles)
Support for the user to extend knowledge of specific interaction within and across applications to other similar situations

Consistency

(Learnability Principles)

Likeness in input - output behavior arising from similar situations or similar task objectives

Dialogue Initiative

(Flexibility Principles)

• Freedom from system imposed constraints on input dialogue

• System vs user pre-emptiveness

• (Ex. a dialog box prohibits the user from interacting with the system in any way that does not direct input to the box)

Multithreading

(Flexibility Principles)

Ability of a system to support user interaction for more than one task at a time

Task migratability

(Flexibility Principles)
Passing responsibility for task execution between user and system

Substitutivity

(Flexibility Principles)

• Allowing equivalent values of input and output to be substituted for each other.

• Representation multiplicity; equal opportunity

Customizability

(Flexibility Principles)

• modifiability of the user interface by user (adaptability) or system (adaptivity)

Adaptability

(Flexibility Principles - Customizability)
The user’s ability to adjust the form of input and output

Adaptivity

(Flexibility Principles - Customizability)
Automatic customization of the ui by the system

Recoverability

(Robustness Principles)

Ability of the user to take corrective action once an error has been recognized

• forward/backward recovery

Responsiveness

(Robustness Principles)
How the user perceives the rate of communication with the system

• system stability

Task Conformance

(Robustness Principles)

The degree which the system can support all of the user’s tasks

• task completeness; task adequacy

Standards

Set by national or international bodies to ensure compliance by a large community of designers. It can apply specifically to either the hardware or the software used to build the interactive system.

ISO 9241

(Standards)

Defines usability as effectiveness, efficiency, and satisfaction with which users accomplish tasks

Effectiveness

(Standards)
The accuracy and completeness with which specified users can achieve specified goals in particular environments

Efficiency

(Standards)
The resources expended in relation to the accuracy and completeness of goals achieved

Satisfaction

(Standards)

The comfort and acceptability of the work system to its users and other people affected by its use

Guidelines

Is more suggestive and general than standards

• Many textbooks and reports full of guidelines

• Abstract guidelines (principles) and detailed guidelines (style guidelines)