1. Suitability for the task
The dialogue is suitable for a task when it supports the user in the effective and efficient completion of the task.
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ISO 9241 Part 110: Dialogue Principles
Interaction principles and design recommendations.
ISO 9241 Part 110 is the international standard that formalizes dialogue principles for interactive systems. Unlike informal heuristics published by individual researchers, this guideline carries the weight of the International Organization for Standardization — which matters when usability is a regulatory, procurement, or compliance requirement.
The standard defines seven interaction principles: suitability for the user's task, self-descriptiveness, conformity with expectations, learnability, controllability, robustness against user errors, and user engagement. Each principle has sub-criteria that an evaluator can audit against.
Teams most often reach for ISO 9241 when they're working on medical devices, government systems, financial services, or B2B products where customers explicitly ask for standards-based UX evaluation in their RFPs. It's also useful internally as an auditable baseline: the standard format means a review done by one team can be defended to a different team, an auditor, or a legal reviewer six months later. Pair it with lighter-weight heuristics like Nielsen's for day-to-day design reviews.
2. Self-descriptiveness
The dialogue is self-descriptive when each dialogue step is immediately comprehensible through feedback from the system or is explained to the user on request.
3. Controllability
The dialogue is controllable when the user is able to initiate and control the direction and pace of the interaction until the point at which the goal has been met.
4. Conformity with user expectations
The dialogue conforms with user expectations when it is consistent and corresponds to the user characteristics, such as task knowledge, education, experience, and to commonly accepted conventions.
5. Error tolerance
The dialogue is error tolerant if despite evident errors in input, the intended result may be achieved with either no or minimal action by the user.
6. Suitability for individualization
The dialogue is capable of individualization when the interface software can be modified to suit the task needs, individual preferences, and skills of the user.
7. Suitability for learning
The dialogue is suitable for learning when it supports and guides the user in learning to use the system.
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ISO 9241 Part 110, on a live URL, in one click.
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