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Design Principles, Guidelines and Metaphor. Howell Istance Department of Computer Science De Montfort University. Objectives. to provide an overview of Norman's model of interaction to distinguish between user model, design model and system image

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design principles guidelines and metaphor

Design Principles, Guidelines and Metaphor

Howell Istance

Department of Computer Science

De Montfort University

objectives
Objectives
  • to provide an overview of Norman's model of interaction
  • to distinguish between user model, design model and system image
  • to explain basis for common design principles in HCI
  • to explain the role of metaphor as one means of building an appropriate user model

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the dmu pabx interface
The DMU PABX interface…

The university installed an well known PABX telephone system - the functionality provided is hardly used at all by staff despite regular attempts to publicise the features by printing and circulating the list of key codes and the actions they cause.

Why it this so….?

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fundamental requirements of good design for use by people
Fundamental requirements of good design for use by people
  • provide a good conceptual model
  • make things visible
  • use easily understood mappings

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affordances and constraints
Affordances and Constraints
  • affordance - the perceived and actual properties of a thing, primarily those fundamental properties that determine just how the thing could possibly be used
  • when affordances are well utilised, the user can easily guess what to do by looking at the thing (no picture, label or instruction is needed)
  • constraints suggest natural limitations in the way in which things can be used

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mapping and feedback
Mapping and Feedback
  • mapping relationship between controls and their movements, and the results in the real world
  • natural mappings utilise physical analogies and cultural standards
    • additive dimensions
    • substitutive dimensions
  • feedback: sending the user information about what action has actually been done and what has been achieved

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norman s theory of action
Norman's Theory of action

(gulf of evaluation)

Interpreted

  • bridging the gulf of execution - designer creates input structures and information displays to fit the psychological needs of the user
  • bridging the gulf of evaluation - user has intentions, creates plans and action sequences in terms of what is required by the system (the way the designer intends the system to be used)

psychological variables

(users knowledge)

physical variables

(controlled by system)

translated into actions

(gulf of execution)

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stages of user activities
Stages of user activities
  • establishing the goal
  • forming the intention
  • specifying the action sequence
  • executing the action
  • perceiving the system state
  • interpreting the state
  • evaluating the state with respect to the goals and intentions

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slide9
(illustration of 7 stage model)

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slide10
(fridge example)

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problems with the refrigerator example
Problems with the refrigerator example
  • matching the psychological variables of interest to the physical variables being controlled - labels on the control mechanism indicate some relationship to the psychological variables, they do not control these directly
  • mapping - strong interaction between controls make a simple mapping between control function and control outcome difficult to establish and represent
  • feedback - very slow
  • conceptual model - none, instructions do not convey an appropriate model

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design model user model and system image

Design

Model

User

Model

Designer

System

Image

System and Documentation

Design Model, User Model and System Image

User

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developing key interface elements
Developing key interface elements
  • develop an appropriate interface metaphor or conceptual model suitable to the user population
  • communicate that model to the user in a consistent manner
  • provide high level task-oriented operations, not low-level implementation commands (bridge the gap of execution)
  • make things visible (if an object has function (behaviour) , the interface should show this)
  • provide informative feedback

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communicating models
Communicating Models

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metaphors
Metaphors
  • can be used to structure a user's mental model to facilitate ease of initial learning
  • use existing knowledge of familiar domains to provide explanations of unfamiliar artifacts
  • many terms in computing rely on common-use metaphors
    • e.g menus, forms, windows
  • provides the designer with a means of building a 'myth' that the system behaves like something the user is already familiar with

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2d spatial metaphors
2D spatial metaphors
  • sheet of paper, forms, spread sheets
  • pages - hold text, images, (magically) moving images
  • drafting table - tools laid out around a working area
  • light table - view many small images at once
  • maps - birds eye view
  • blackboards and whiteboards

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2 1 2 spatial metaphors
2 1/2 spatial metaphors
  • uses several layers of stacked 2D surfaces -each congruent with the overall metaphor
  • desktops and briefcases
  • books
  • Notebooks
  • Index Cardfiles , NoteCards
  • Doors and Rooms

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macintosh desktop
Macintosh Desktop

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leads to a full wastebasket
....leads to a full wastebasket

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components of notecards
Components of NoteCards

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3d metaphors
3D metaphors
  • virtual worlds
  • buildings

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metaphors based on human activity
Metaphors based on human activity
  • Visiting a supermarket, museum, eating in a restaurant
  • agents - someone who does a task on behalf of someone else
  • stage and theatre as spatial metaphor

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tension between literalism and magic
Tension between literalism and magic
  • literal interpretation of the spreadsheet would use an on-screen calculator to sum columns of values for the user to type back into the spreadsheet
    • maximises understanding but does not add power
  • magic interpretation - rows and columns magically sum themselves and then display values
    • maximises power but may interfer with understanding

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strengths in the use of metaphors
Strengths in the use of metaphors
  • a strength of using metaphors is that they can suggest behaviours to the user based on their knowledge of the familiar domain and encourage exploratory learning of the new artefact
    • e.g.. if I throw a file into a waste-basket, I should be able to pick it out again, Now how do I do that ...?

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limitations in the use of metaphors
Limitations in the use of metaphors
  • by definition, each metaphor has a limitation - one single metaphor is unlikely to represent all aspects of system behaviour
  • leads to the use of composite metaphors e.g. windows and desk-tops
  • user has to be encouraged to use relevant parts of the analogy
  • care has to be taken that the metaphor does not suggest behaviours that can lead to errors

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process of generating metaphors after erickson
Process of generating metaphors (after Erickson)
  • Define and understand the functionality offered by the system
  • Observe users understanding of the artifact and identify problems they have
  • Generate metaphors
  • Evaluate candidate metaphors using:
    • Amount of structure metaphor offers
    • Applicability of structure to artifact
    • Representability
    • Suitability to audience
    • Extensibility

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macintosh guidelines
metaphor based

direct manipulation

see and point

consistency

WYSIWYG

user control

feedback and dialogue

forgiveness

perceived stability

aesthetic integrity

modelessness

MacIntosh Guidelines

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alternative principles genter and neilsen
Alternative Principles (Genter and Neilsen)
  • central role of language
  • rich internal representation of objects
  • more expressive interface
  • expert users
  • shared control

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