ISO’s dialogue principles (2020)

The ISO standard 9241-110 from 2020 defines seven dialogue principles:
#1: Suitability for the user’s tasks
#2: Self-descriptiveness
#3: Conformity with user expectations
#4: Learnability
#5: Controllability
#6: Use error robustness
#7: User engagement

The principles and the explanations of the principles are taken from the ISO standard. The Personal comments and the examples are my own.

The principles are more complex than they appear at first glance. In the standard, each of the seven principles is divided into categories of recommendations. Each recommendation is illustrated by 2-3 examples. The full description of the seven principles, 20 categories of recommendations, 65 recommendations, and about 140 examples take up 15 densely printed pages in the standard. The standard is not freely available; it is available for purchase.

#1: Suitability for the user’s tasks

An interactive system is suitable for the user’s tasks when it supports the users in the completion of their tasks, i.e. when the operating functions and the user-system interactions are based on the task characteristics (rather than the technology chosen to perform the task).

Personal comment: To me, this principle is “Meeting user needs”, which unfortunately is covered neither by Molich and Nielsen’s heuristics (1990) nor by Nielsen’s heuristics (1994).


  • The home page of a university website displays links to information about faculty members’ phone numbers and emails, application forms, academic calendar, and a department/course list, rather than campus photo slide show, alumni in the news, letter from the president, and a statement of the school’s philosophy
  • A ticket machine accepts payment by credit card and cash rather than by cash only
  • A newspaper website presents search results based on relevance for the main target group rather than by date

#2: Self-descriptiveness

The interactive system presents appropriate information, where needed by the user, to make its capabilities and use immediately obvious to the user without unnecessary user-system interactions.


  • Display available key actions clearly: The home page of an app for a pet adoption service clearly and briefly describes the purpose of the app and provides an overview of the five key functions offered by the app: The adoption process, Adopt a dog, Stories from users who adopted a dog, Donate, Help
  • Show limitations: A ticket machine for train tickets clearly states that it only accepts credit cards (no cash) and provides a list of the accepted credit cards
  • Break up complicated transactions: The Danish citizen service website ( divides the process of completing a marriage application into simple, clearly described steps. Each step is described in plain language in some detail (the wizard pattern).
  • Provide feedback: A navigation system indicates to the user that it is currently not connected to a satellite and that the displayed location information may be incorrect.

#3: Conformity with user expectations

The interactive system’s behavior is predictable based on the context of use and commonly accepted conventions in this context.


  • Common conventions: The website of an airline consistently displays the company logo in the upper left corner of each web page. Clicking the logo causes the website to display the home page.
  • Speak the users’ language: A car rental website only uses words that are understood by users without any particular knowledge about renting cars. Whenever the use of technical terms is unavoidable, the meaning of the words are explained in a pop-up with examples.
  • Consistency: In an organisation, all systems consistently use the same phrases for login, for example “user name” (not user-id), and “password” (not access key)

#4: Learnability

The interactive system supports discovery of its capabilities and how to use them, allows exploration of the interactive system, minimizes the need for learning and provides support when learning is needed.

Learnability involves guidance related to discovery of information and controls that users are looking for; exploration of information and controls that users have discovered; and retention of information about the system

Personal comment: Learnability is closely related to the other principles, in particular self-descriptiveness and use error robustness.


  • Discovery: A hotel booking app clearly displays the functions that are of most interest to users on the home page: Book a room; Modify a reservation; Cancel a reservation; Special deals; Property reviews
  • Safe exploration: A word processing system allows users to undo all their actions since they first started working on a document, even if considerable time has passed
  • Inline help: On a hotel booking website, controls that may be difficult to understand, for example “Security code” are followed by a “?”. Terms that may be difficult to understand are underlined. Clicking a “?” or an underlined term produces an explanation in plain language.
  • Relevant examples and templates: A job search website offers the user examples of job applications and CVs that can be easily used or modified.

#5: Controllability

The interactive system allows the user to maintain control of the user interface and the interactions, including the speed and sequence and individualization of the user-system interaction.


  • Interruption by the user: An antivirus program that is scanning a hard disk drive for viruses can be stopped at any point of time by the user pressing a prominent stop button.
  • No surprises: On a newspaper website, a video starts playing only when the user explicitly starts the video. Per default, audio is turned off.
  • Flexibility: In an online questionnaire, users freely decides in what order they want to answer questions. Users can store a draft of their answers and complete the questionnaire later on.
  • Undo: A word processing system allows users to undo all their actions since they first started working on a document, even if considerable time has passed
  • Individualization: On a hotel booking website, the user can set the language and currency used by the website. The website remembers the choices for future visits by the user.

#6: Use error robustness

The interactive system assists the user in avoiding errors and in case of identifiable errors treats them tolerantly and assists the user when recovering from errors. Use error robustness involves guidance related to use error avoidance; use error tolerance; use error recovery.

Personal comment: This is three separate principles: error avoidance; error tolerance; and error recovery. For political reasons the ISO Committee combined them into one principle.
Any time you deal with errors, imagine how a human being would handle the error – most human beings try to avoid errors, tolerate errors, and provide good error recovery.

Examples for error avoidance:

  • Include helpful constraints: On a flight booking website, users enter dates by clicking on a graphic calendar rather than entering the date using the keyboard
  • Prevent well-known problems: A car rental website does not allow the user to enter a pick-up time where the rental office is closed; it provides an appropriate explanation why the pick-up time is not available. The website provides a warning if the user selects a return time when the rental office is closed, provided that the rental office allows after-hours return of rented cars.
  • Provide clear feedback: When entering a password, the user has the option of having the password displayed in clear text if the user decides that the environment is safe
  • Provide helpful suggestions: Search suggestions provided by an e-commerce website enable users to type less, thereby making fewer slips or mistakes that would produce no results.

Examples for error tolerance:

  • Allow the user to regret mistakes: A drawing application offers users undo and redo functions, so any mistake can easily be corrected
  • Support error recovery: A file management system keeps a copy of a file that the user has deleted, in case the user finds out that they deleted the file by mistake.
  • Accept incorrect input if the user’s intention is clear: The user enters a date in a format that is not the official format used by the website, for example 15 may 2020 instead of 15-05-2020; the website converts the input to the correct format without bothering the user with a message.

Examples for error recovery: See the separate page about Error messages

#7: User engagement

The interactive system presents functions and information in an inviting and motivating manner supporting continued interaction with the system.

Personal comment: Adherence to the previous dialogue principles is an important precondition for user engagement. User engagement must be done in an ethical manner; some aspects of user engagement are inappropriate for some interactive systems, for example sports betting websites.


  • Build trust: An e-commerce website clearly displays its physical address and contact information together with pictures and biographies of key people. It also links to independent mentions and reviews of the company, for example in newspapers.
  • Assure the user that everything looks OK: An anti-virus program displays a clear assurance “You are protected” together with a large, green checkmark and the link “More information”.
  • Anticipate user needs that the user may not be aware of: A web shop provides the opportunity for passionate support staff, who know users’ questions and demands, to input product descriptions instead of just automatically republishing the manufacturer specifications.


The definitions and some of the examples are taken from the ISO 9241-110 standard and from the CPUX-F curriculum. The CPUX-F curriculum is freely available on

Text from the draft international standard ISO/FDIS 9241-110.2020 is reproduced with permission from Danish Standards Foundation (DS).