Lectures for the course "Ergonomics applied to the usability of web pages and apps" held at the School of design of Politecnico di milano in the first semester of 2021-2022 academic year

1. 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

2. www.dadda.it roberto@dadda.it Excellence in usability 1st semester 2021-2022 2
Errors handling

3. www.dadda.it roberto@dadda.it Excellence in usability 1st semester 2021-2022 3
• Mitigate errors –
eliminate or lessen the
consequences of error.
• Trap errors – detect
errors when they occur.
• Avoid errors – reduce
the opportunity for
error.

4. www.dadda.it roberto@dadda.it Excellence in usability 1st semester 2021-2022 4
Error, not a simple concept
•No simple dichotomy between errors and
correct actions
•Error is not a single side concept

5. www.dadda.it roberto@dadda.it Excellence in usability 1st semester 2021-2022 5
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.”

6. www.dadda.it roberto@dadda.it Excellence in usability 1st semester 2021-2022 6
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.

7. www.dadda.it roberto@dadda.it Excellence in usability 1st semester 2021-2022 7
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.

8. www.dadda.it roberto@dadda.it Excellence in usability 1st semester 2021-2022 8

9. www.dadda.it roberto@dadda.it Excellence in usability 1st semester 2021-2022 9

10. www.dadda.it roberto@dadda.it Excellence in usability 1st semester 2021-2022 10
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

11. www.dadda.it roberto@dadda.it Excellence in usability 1st semester 2021-2022 11
prevention

12. www.dadda.it roberto@dadda.it Excellence in usability 1st semester 2021-2022 12
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

13. www.dadda.it roberto@dadda.it Excellence in usability 1st semester 2021-2022 13
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”

14. www.dadda.it roberto@dadda.it Excellence in usability 1st semester 2021-2022 14
Avoid where possible and when not
possible give good indications

15. www.dadda.it roberto@dadda.it Excellence in usability 1st semester 2021-2022 15

16. www.dadda.it roberto@dadda.it Excellence in usability 1st semester 2021-2022 16

17. www.dadda.it roberto@dadda.it Excellence in usability 1st semester 2021-2022 17
Obliging functions: Car door locking

18. www.dadda.it roberto@dadda.it Excellence in usability 1st semester 2021-2022 18
Good use of default

19. www.dadda.it roberto@dadda.it Excellence in usability 1st semester 2021-2022 19

20. www.dadda.it roberto@dadda.it Excellence in usability 1st semester 2021-2022 20
Alert staging…
Note alert box
(Livello 1)
Caution alert box
(Livello 2)
Stop alert box
(Livello 3)

21. www.dadda.it roberto@dadda.it Excellence in usability 1st semester 2021-2022 21
Get confirmations

22. www.dadda.it roberto@dadda.it Excellence in usability 1st semester 2021-2022 22
Without exaggerations to avoid blindness

23. www.dadda.it roberto@dadda.it Excellence in usability 1st semester 2021-2022 23
Offer
sure
bypass

24. www.dadda.it roberto@dadda.it Excellence in usability 1st semester 2021-2022 24
The three stages of error handling

25. www.dadda.it roberto@dadda.it Excellence in usability 1st semester 2021-2022 25
1 alert

26. www.dadda.it roberto@dadda.it Excellence in usability 1st semester 2021-2022 26
2 Identify

27. www.dadda.it roberto@dadda.it Excellence in usability 1st semester 2021-2022 27
3 Direct

28. www.dadda.it roberto@dadda.it Excellence in usability 1st semester 2021-2022 28

29. www.dadda.it roberto@dadda.it Excellence in usability 1st semester 2021-2022 29
Undo

30. www.dadda.it roberto@dadda.it Excellence in usability 1st semester 2021-2022 30

31. www.dadda.it roberto@dadda.it Excellence in usability 1st semester 2021-2022 31
Error 404, important to manage it!

32. www.dadda.it roberto@dadda.it Excellence in usability 1st semester 2021-2022 32
Usability
Roberto DADDA
roberto@dadda.it
www.dadda.it
Skype, Facebook e Twitter robertodadda