Design Principles, Guidelines and Metaphor Howell Istance Department of Computer Science De Montfort...
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Transcript of Design Principles, Guidelines and Metaphor Howell Istance Department of Computer Science De Montfort...
Design Principles, Guidelines and Metaphor
Howell Istance
Department of Computer Science
De Montfort University
SOFT3057 - Interactive Systems
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 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
provide a good conceptual model make things visible use easily understood mappings
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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 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
bridging the gulf of execution - des igner creates input structures and information displays to f it the psychological needs of the user
bridging the gulf of evaluation - user has intentions, c reates plans and action sequences in terms of what is required by the system (the way the des igner intends the system to be used)
Interpreted
psychological variables(users knowledge)
physical variables(controlled by system)
translated into actions
(gulf of evaluation)
(gulf of execution)
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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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(illustration of 7 stage model)
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(fridge example)
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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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UserModel
DesignModel
Design Model, User Model and System Image
Designer User
System and Documentation
SystemImage
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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
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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
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
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
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....leads to a full wastebasket
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Components of NoteCards
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3D metaphors
virtual worlds buildings
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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
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
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
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)
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
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Alternative Principles (Genter and Neilsen)
central role of language
rich internal representation of objects
more expressive interface
expert users
shared control