Taskbased user interface principles

1
Task-based user interface principles

• Fraser Hamilton
• Brighton University
• F.Hamilton_at_bton.ac.uk

2
The story so far

• What are principles?
• S Laws
• D Attributes that contribute to usability
• E Prescriptions to enable performance guarantees
• Why bother?
• To inform design decision making
• Steamline development. Reduce iteration.
• Reuse knowledge
• Reduce business risk. (More predictable.)

3
Remember this?

• Science
• Factors that matter psychology, e.g. redundancy
• Design
• Guidelines, e.g. Dont use colour without
• Principles, e.g. flexibility, recoverability
• Engineering
• Users, Tasks, Machines, Performance.
• Highly specific advice

4
Bringing home the bacon

• Guide designers in making design decisions
• Know the consequences of decisions
• Relevant to design practice and usability
• Validated consequences should be known
• Predictive predicted in this context (UTM)
• Scoped set of applicable design problems
• Prescriptive inform design
• Operational techniques to apply them

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Task based design
Existing users and artefacts
Current task model
Envisioned task model
User interface design

• Design decisions must be made
• What tasks are essential? Omitted?
• How should tasks be allocated?
• Structure goals/subgoals, object relations
• Representation of objects
• How can we inform these decisions?
• Performance learning, usage, improve task output

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The Analysis-Design gulf

• TA produces descriptions
• The problem How to use descriptions of user
  tasks to design systems
• Descriptions Systems
• goals screen layout
• tasks widgets
• objects command names

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What you must know

• What are the principles?
• What is their theoretical base?
• How do they inform interface design?
• Scope Users, Tasks, Machines (i.e. UTM)
• How do they improve performance?
• How were they validated?
• How easy would it be for designers to use them?

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Task Knowledge Structures (TKS)

• Tasks
• activity, agents, state
• grouped by roles

Fraser (Lecturer)
Researcher
Tutor
Consultant
Prepare lectures
Visit students
Hold supervision meetings
Mark assignments
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TKS Objects

• Describe users knowledge of objects in a domain

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Brighton Rock
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Human Computer Interaction
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TKS Goals

• Describe users knowledge of goals
• Hierarchy, control relations

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11
The principles

• Taxonomic categorisation
• Actions on same/similar objects chunk into a
  subgoal
• Sequential dependency
• Actions sequentially related chunk into a subgoal
• Easier recall of items, performance benefits

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Results Task times

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Results task errors

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How good is the bacon?

• Theory TKS categorisation
• Relevant TA, structure, GUI design
• Validated experiments
• Predictive predict learning difficulties
• Scoped existing domain K. Gui
• Prescriptive TA P -gt TM -gt GUI
• Operational Hmm? What objects? Rep?

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Unprincipled task model

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Unprincipled design

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Sequential dependency condition

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Principled task model

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Principled GUI