Chapter 2

Guidelines, Principles, and Theories

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User-interface designers have organized their experience and research into a collection of guidelines, principles, and theories.

  • Guidelines give designers specific recommendations for creating good designs and avoiding bad ones.
  • Principles bridge the gap between theory and guidelines, acting as practical ways to compare and judge design alternatives.
  • Theories are useful to describe objects and actions in interface design. Theories can also be useful as predictive instruments of user behaviors and designs.

The use of each of these can provide designers with ways to improve existing interfaces and can prevent poor designs from being created.


Guidelines are concrete and specific rules for designing interfaces based on an organization's or an individual's experience and/or reasoning. This is a strength because it gives developers a shared set of standards to work with. However, many guidelines are criticized for being too specific , difficult to apply, or at times wrong. Most designers do agree that discussion of guidelines is required to promote awareness of best practices. The book has four sections of examples, and many of the sections have overlapping examples.

Guidelines that kept reoccurring in each example

  • Use predictable and consistent standards for navigation, displaying data, data entry, and tasks
  • Minimize the memory load placed on users by limiting tasks to as few steps as possible, displaying only information relevant or useful to the task(s) at hand, and do not require users to remember complex commands or large sets of data
  • Allow users to choose what information is displayed and how it is displayed and formatted where possible
  • Limit the ways you draw attention to data so that users are not overwhelmed and the interface does not become cluttered
  • Format information so that the way it was entered can be understood and provide data inputs that easily translate into how the information will be displayed
  • Provide users with disabilities alternatives to the interface

Creating guideline documentation is a good way for designers to make their experience and intuition accessible to others. However, processes need to be in place that educate designers and enforce guidelines, as well as determine the exemption and enhancement of guidelines.


The text discusses the following principles:

  • Determine users' skill levels
    • Novice/First-time users
    • Knowledgeable intermittent users
    • Expert frequent users
  • Identifying the tasks
    • High-level actions can be divided into multiple mid-level actions that can be further divided into smaller atomic actions. It is the atomic actions that are most important to interface design. Making the atomic actions to specific can result in user frustration as they have to perform so many small actions to complete a high-level action. The reverse of this also results in user dissatisfaction since larger atomic actions may prevent users from getting what they want from the system, or force users to rely on a larger numbers of actions with specialized options.
  • Choose an interaction style
    • Direct manipulation
    • Menu selection
    • Form fill-in
    • Command language
    • Natural language
    • box2.1, pg. 67 - Shows pros and cons of each interaction style
    • box2.2, pg. 68 - Shows a progression of interfaces leading to more direct manipulation
  • Eight Golden Rules of interface design
    • Strive for consistency
    • Cater to universal usability
    • Offer informative feedback
    • Design dialogs to yield closure
    • Prevent errors
    • Permit easy reversal of actions
    • Support internal locus of control
    • Reduce short-term memory load (which the book does not)
  • Prevent errors
    • Error prevention is the 5th golden rule but its importance warrants a section of its own.
      • Understand the nature of errors
      • Provide feedback about the state of the interface
      • Design consistent actions
      • Correct actions
      • Complete sequences
  • Ensuring human control while increasing automation
    • box2.3, pg. 74 - Comparison of humans and machine capabilities
    • Human supervision is necessary for automation because the real world is and open system and the computer is a closed system. It is nearly impossible to determine and program all possible outcomes of an action, so humans are needed to judge the unforeseen events.
    • Agent Scenario
      • Microsoft BOB and Clippy
    • Avatars
      • Second Life
    • User Model (Adaptive Interface)
      • The system is able to keep track of the user's actions and performance and adapt the interface to best suit the user. However, the changes must not significantly alter the way the user completes his/her tasks.
      • Google Search Results
      • Recommender systems or collaborative filtering
        • suggestions
    • Control-Panel Model
      • Gives the user a sense of control over the system


  • Theories fall under several different categories:
    • Descriptive (consistency)
    • Explanatory (sequences of actions)
    • Prescriptive (guidance)
    • Predictive (comparison among designs)
    • Theory Skills
      • Perceptual – What do you sense?
      • Cognitive – What do you think?
      • Motor - What are you doing? (Physical)
  • Taxonomy - Ordering a set of phenomena or users into meaningful categories.
  • Theories should:
    • be central to both research and practice
      • Guide researchers in understanding concepts
      • Guide practitioners in making design decisions
    • lead practice rather than lag behind

Design by levels

One method to developing descriptive theories is to break down concepts into separate levels.

  • Four-Level Approach
    • Conceptual level – a user’s mental perception of the system.
    • Semantic level – the meanings conveyed by the user's actions and the output displayed by the system
    • Syntactic level – the “complete sentences” that are formed from user actions to convey semantics that are inherent to the system. This is the level in which the user takes action
    • Lexical level – The precise method that is used by users to specify the syntax. Menu items, colors, buttons, mouse icons, etc
  • Designers need to decompose objects as well as complex actions
  • Predictive Approach - Tasks can be divided into a series of actions which can help the designers predict the amount of time required to perform the specific task.
    • Goals, Operators, Methods, and Selection Rules (GOMS) - goals can be decomposed into several operators (actions) and then further divided into methods. Selection Rules can also be applied to obtain alternate methods for achieving a goal.

Stages-of-action models

The steps that the user must take in order to accomplish a task.

  • Norman's 7 stages of action (cycles of action and evaluation):
    • Forming the goal
    • Forming the intention
    • Specifying the action
    • Executing the action
    • Perceiving the system state
    • Interpreting the system state
    • Evaluating the outcome
  • Norman also suggests four principles of good design:
    • the state and action alternatives should be visible.
    • there should be a good conceptual model with a consistent system image.
    • the interface should include good mappings that show the relationship between stages.
    • users should receive continuous feedback.
  • makes the complex checkout process comprehensible by dividing it into a four-part process:
    • (1)Sign-in; (2) Shipping & Payment; (3) Gift-Wrap; (4) Place Order


Consistency is very important for a successful interface.

  • Consistency is necessary in all aspects if the interface including:
    • terminology for objects and actions
    • colors
    • layout
    • icons
    • fonts
    • buttons, etc.

However, sometimes inconsistency is required to draw attention to a specific possibly dangerous action.

Contextual theories

The context in which the user completes an action has a crucial effect on the nature of the action that has been preformed.
These theories are very important to mobile devices and ubiquitous computing innovations.

  • A taxonomy for mobile device applications:
    • Monitor and alert
    • Gather and spread
    • Participate and relate
    • Locate and identify
    • Capture and share

Contextual theories are developed by observing users in their own environment and interacting with them. These theories include every aspect of the users and the environment in which the they will be interacting with the system. Because this information is very hard to obtain using a controlled experiment, many researchers have shifted their research away from this type of experimentation and have started to focus more on ethnographic observation, focus-groups, and long-term case studies.


Design guidelines and principles are becoming more important and understood in the community of designers today. Both of them are emerging from practical experience and studies created to monitor users. People in the field of design are able to view already available guideline documents and then create their own based on the experience and settings they have. It is important for designers to remember the guidelines recognized by the public and those created for the project/company should help shape any interface. Consistency, reduced errors, and automation are all also very important to the design process and should be looked at carefully as well as planned for by the designer(s). Some principles have become more accepted than others such as preventing errors, but each one may require some new interpreting due to new and/or improved technologies emerge into the market. Automation can be a great asset to an application because it takes away user control and thus prevents possible user errors. Any successful designer must go through an extensive process in developing a unique interface that should include examination of the requirements, task analysis, and specifications of the user population. Designers also have to take into consideration the systems that expert users, with established sequences of actions, operate will have to have reduced time required to take each step. Whereas systems that novice users operate need to have a focus on task objects and actions so they can be learned easily while promoting the confidence level for the users.

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