Software Engineering: User Interface Design & its golden rules

User Interface Design & its golden rules

User interface design creates an effective communication medium between a human and a computer.

(1) Place the user in Control.

As a designer, you may be tempted to introduce constraints and limitations to simplify the implementation of the interface.

The result may be an interface that is easy to build, but trying to use.

Mandel defines a number of design principles that allow the user to maintain control:

Define interaction modes in a way that does not force a user into unnecessary or undesired actions.
Provide for flexible interaction

Because different users have different interaction preferences, choices should be provided. For example, software might allow a user to interact via keyboard commands, mouse movement, a digitizer pen

Allow user interaction to be interruptible and undoable.

When involved in a sequence of actions, the user should be able to interrupt the sequence to do something else (without losing the work that had been done).
The user should also be able to “undo” any action.

Streamline interaction as skill levels advance and allow the interaction to be customized.

Users often find that they perform the same sequence of interactions repeatedly.

Hide technical internals from the casual user.

The user should not be aware of the operating system, file management functions, or other arcane computing technology. In essence, the interface should never require that the user interact at a level that is “inside” the machine (e.g., a user should never be required to type operating system commands from within application software)

Design for direct interaction with objects that appear on the screen.

For example, an application interface that allows a user to “stretch” an object (scale it in size) is an implementation of direct manipulation.

(2) Reduce the User’s Memory Load

The more a user has to remember, the more error-prone the interaction with the system will be.

It is for this reason that a well-designed user interface does not tax the user’s memory.

Mandel defines design principles that enable an interface to reduce the user’s memory load…

Reduce demand on short-term memory.

The interface should be designed to reduce the requirement to remember past actions, inputs, and results. This can be accomplished by providing visual cues that enable a user to recognize past actions, rather than having to recall them

Establish meaningful defaults :

The initial set of defaults should make sense for the average user, but a user should be able to specify individual preferences. However, a “reset” option should be available, enabling the redefinition of original default values.

Define shortcuts that are perceptive.

When mnemonics are used to accomplish a system function (e.g., alt-P to invoke the print function), the mnemonic should be tied to the action in a way that is easy to remember (e.g., first letter of the task to be invoked)

The visual layout of the interface should be based on a real-world metaphor (Symbol / Image).

This enables the user to rely on well-understood visual cues, rather than memorizing an hidden interaction sequence.

Disclose information in a progressive fashion :

The interface should be organized hierarchically. That is, information about a task, an object, or some behavior should be presented first at a high level of abstraction. More detail should be presented after the user indicates interest with a mouse pick. [Similar like combo box control.]

(3) Make the Interface Consistent :

(1) All visual information is organized according to design rules that are maintained throughout all screen displays,
(2) Input mechanisms are constrained to a limited set that is used consistently throughout the application,
(3) Mechanisms for navigating from task to task are consistently defined and implemented.

Mandel defines a set of design principles that help make the interface consistent.

Allow the user to put the current task into a meaningful context.

Many interfaces implement complex layers of interactions with dozens of screen images.
It is important to provide indicators (e.g., window titles, graphical icons, consistent color coding) that enable the user to know the context of the work at hand.

Maintain consistency across a family of applications :

A set of applications (or products) should all implement the same design rules so that consistency is maintained for all interaction.
If past interactive models have created user expectations, do not make changes unless there is a compelling reason to do so.
Once a particular interactive sequence has become a standard (e.g., the use of Ctrl + S to save a file), the user expects this in every application he encounters.
A change (e.g., using Ctrl + S to invoke scaling) will cause confusion.