11 error management

www.dadda.it roberto@dadda.it Excellence in usability 1st semester 2021-2022 1
ERGONOMICS APPLIED TO THE DESIGN OF USABLE WEB
PAGES AND APPS
Roberto DADDA and Paolo NEGRI

Errors handling

• Mitigate errors –
eliminate or lessen the
consequences of error.
• Trap errors – detect
errors when they occur.
• Avoid errors – reduce
the opportunity for
error.

Error, not a simple concept
•No simple dichotomy between errors and
correct actions
•Error is not a single side concept

Donald Norman
“The designer shouldn't think of a
simple dichotomy between errors
and correct behavior; rather, the
entire interaction should be
treated as a cooperative
endeavor between person and
machine, one in which
misconceptions can arise on
either side.”

Error tollerance
• The ultimate goal is a system which has no errors. But, product
developers are human, and computer systems far from perfect, so
errors may occur. An error tolerant program is designed to prevent
errors caused by the user’s interaction, and to help the user in
recovering from any errors that do occur.

Goals
• Make it difficult to take incorrect actions. Design links and buttons to be
distinctive, use clear language, avoiding technical jargon, and be sure that
dependent fields or choices appear together.
• Make it difficult to take invalid actions. Limit choices when possible to
those which are correct, provide clear examples for data entry, present
only appropriate navigation options.
• Make it difficult to take irreversible actions. Provide the ability to back
track, provide means to undo or reverse actions, avoid dead-end screens.
Don’t indiscriminately use confirmations – users become insensitive to
them.
• Plan for the unexpected. Allow for users to add new entries, take
exceptional routes through the interface or make choices you did not
predict. Be polite about "correcting" mistakes that may arise from this lack
of foresight.

Design for error
• Prevention
• Discover and facilitate correction
• Make where possible available an UNDO
• Change attitude: error not as a stop, error
as deviation form path to success

prevention

Avoid modality!
• In user interface design, a mode is a distinct setting within a
computer program or any physical machine interface, in which the
same user input will produce perceived different results than it
would in other settings

Modality
• "An human-machine interface is modal with
respect to a given gesture when (1) the
current state of the interface is not the
user's locus of attention and (2) the
interface will execute one among several
different responses to the gesture,
depending on the system's current state.“
Jef Raskin, “The humaninterface”

Avoid where possible and when not
possible give good indications

Obliging functions: Car door locking

Good use of default

Alert staging…
Note alert box
(Livello 1)
Caution alert box
(Livello 2)
Stop alert box
(Livello 3)

Get confirmations

Without exaggerations to avoid blindness

Offer
sure
bypass

The three stages of error handling

1 alert

2 Identify

3 Direct

Undo

Error 404, important to manage it!

Usability
Roberto DADDA
roberto@dadda.it
www.dadda.it
Skype, Facebook e Twitter robertodadda

11 error management

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