User interfaces of interactive systems, such as websites or software, should be easy to operate by the user. Part 110 of DIN EN ISO 9241 describes the following principles for the design and assessment of an interface between user and system (dialog design).
Although the following seven dialog design principles were defined in 1999, they are still valid today.
- Task suitability: The dialog helps the user to perform his/her task effectively and efficiently.
- Self-descriptiveness: Each dialog step is immediately comprehensible through feedback from the application or is explained to the user on request.
- Controllability: The user is able to start the dialog flow and to influence its direction and speed until the goal is reached.
- Conformity with expectations: The dialog is consistent and corresponds to the user's characteristics, for example, the knowledge gained from the user's work area, training and experience, as well as the generally accepted conventions.
- Fault tolerance: The user can achieve the intended work results despite clearly faulty input with either no or minimal corrections. Despite the faulty input, the application allows the user to achieve the intended objective with minimal corrections. Fault tolerance in usability is a seamless continuation of the fault tolerance principle in accessibility.
- Customizability: The application allows adjustments based on the requirements of the task, individual user preferences and user skills.
- Suitability for learning: Dialog helps the user to learn the system and provides guidance.