User Interface (UI)

User interface design is the design of computers, appliances, machines, mobile communication devices, software applications, and websites with the focus on the user’s experience and interaction.


The goal of user interface design is to make the user’s interaction as simple and efficient as possible, in terms of accomplishing user goals—what is often called user-centered design. Good user interface design facilitates finishing the task at hand without drawing unnecessary attention to itself. Graphic design may be utilized to support its usability. The design process must balance technical functionality and visual elements (e.g.,mental model) to create a system that is not only operational but also usable and adaptable to changing user needs.


Interface design is involved in a wide range of projects from computer systems, to cars, to commercial planes; all of these projects involve much of the same basic human interactions yet also require some unique skills and knowledge. As a result, designers tend to specialize in certain types of projects and have skills centered around their expertise, whether that be software design, user research, web design, or industrial design.



There are several phases and processes in the user interface design, some of which are more demanded upon than others, depending on the project. (Note: for the remainder of this section, the word system is used to denote any project whether it is a web site, application, or device.)


  • Functionality requirements gathering – assembling a list of the functionality required by the system to accomplish the goals of the project and the potential needs of the users.


  • User analysis – analysis of the potential users of the system either through discussion with people who work with the users and/or the potential users themselves.


Typical questions involve:


    • What would the user want the system to do?
    • How would the system fit in with the user’s normal workflow or daily activities?
    • How technically savvy is the user and what similar systems does the user already use?
    • What interface look & feel styles appeal to the user?


  • Information architecture – development of the process and/or information flow of the system (i.e. for phone tree systems, this would be an option tree flowchart and for web sites this would be a site flow that shows the hierarchy of the pages).


  • Prototyping – development of wire frames, either in the form of paper prototypes or simple interactive screens. These prototypes are stripped of all look & feel elements and most content in order to concentrate on the interface.


  • Usability testing – testing of the prototypes on an actual user—often using a technique called think aloud protocol where you ask the user to talk about their thoughts during the experience.


  • Graphic Interface design – actual look & feel design of the final graphical user interface (GUI). It may be based on the findings developed during the usability testing if usability is unpredictable, or based on communication objectives and styles that would appeal to the user.


In rare cases, the graphics may drive the prototyping, depending on the importance of visual form versus function. If the interface requires multiple skins, there may be multiple interface designs for one control panel, functional feature or widget. This phase is often a collaborative effort between a graphic designer and a user interface designer, or handled by one who is proficient in both disciplines.


User interface design requires a good understanding of user needs.



The dynamic characteristics of a system are described in terms of dialogue requirements contained in seven principles of part 10 of the ergonomics standard, the ISO 9241. This standard establishes a framework of ergonomic “principles” for the dialogue techniques with high-level definitions and illustrative applications and examples of the principles. The principles of the dialogue represent the dynamic aspects of the interface and can be mostly regarded as the “feel” of the interface.


The seven dialogue principles are:


  • 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.


  • 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.


  • 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.


  • 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.


  • 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.


  • 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.


  • Suitability for learning: the dialogue is suitable for learning when it supports and guides the user in learning to use the system.


The concept of usability is defined in Part 11 of the ISO 9241 standard by effectiveness, efficiency, and satisfaction of the user.


Part 11 gives the following definition of usability:

  • Usability is measured by the extent to which the intended goals of use of the overall system are achieved (effectiveness).
  • The resources that have to be expended to achieve the intended goals (efficiency).
  • The extent to which the user finds the overall system acceptable (satisfaction).


Effectiveness, efficiency, and satisfaction can be seen as quality factors of usability. To evaluate these factors, they need to be decomposed into sub-factors, and finally, into usability measures.


The information presentation is described in Part 12 of the ISO 9241 standard for the organization of information (arrangement, alignment, grouping, labels, location), for the display of graphical objects, and for the coding of information (abbreviation, color, size, shape, visual cues) by seven attributes. The “attributes of presented information” represent the static aspects of the interface and can be generally regarded as the “look” of the interface. The attributes are detailed in the recommendations given in the standard. Each of the recommendations supports one or more of the seven attributes.


The seven presentation attributes are:


  • Clarity: the information content is conveyed quickly and accurately.
  • Discriminability: the displayed information can be distinguished accurately.
  • Conciseness: users are not overloaded with extraneous information.
  • Consistency: a unique design, conformity with user’s expectation.
  • Detectability: the user’s attention is directed towards information required.
  • Legibility: information is easy to read.
  • Comprehensibility: the meaning is clearly understandable, unambiguous, interpretable, and recognizable.



The user guidance in Part 13 of the ISO 9241 standard describes that the user guidance information should be readily distinguishable from other displayed information and should be specific for the current context of use.


User guidance can be given by the following five means:


  • Prompts indicating explicitly (specific prompts) or implicitly (generic prompts) that the system is available for input.
  • Feedback informing about the user’s input timely, perceptible, and non-intrusive.
  • Status information indicating the continuing state of the application, the system’s hardware and software components, and the user’s activities.
  • Error management including error prevention, error correction, user support for error management, and error messages.
  • On-line help for system-initiated and user initiated requests with specific information for the current context of use.


Research–Past and Ongoing

User interface design has been a topic of considerable research, including on its aesthetics.In the past standards have been developed, as far back as the eighties for defining the usability of software products.One of the structural basis has become the IFIP user interface reference model. The model proposes four dimensions to structure the user interface:


  • The input/output dimension (the look)
  • The dialogue dimension (the feel)
  • The technical or functional dimension (the access to tools and services)
  • The organizational dimension (the communication and co-operation support)


This model has greatly influenced the development of the international standard ISO 9241 describing the interface design requirements for usability. The desire to understand application-specific UI issues early in software development, even as an application was being developed, led to research on GUI rapid prototyping tools that might offer convincing simulations of how an actual application might behave in production use.Some of this research has shown that a wide variety of programming tasks for GUI-based software can, in fact, be specified through means other than writing program code.

Research in recent years is strongly motivated by the increasing variety of devices that can, by virtue of Moore’s Law, host very complex interfaces.

There is also research on generating user interfaces automatically, to match a user’s level of ability for different kinds of interaction.

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