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Task-based user interface principles

Fraser HamiltonBrighton University

F.Hamilton@bton.ac.uk

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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.)

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Remember this?

Science Factors that matter: psychology, e.g. redundancy

Design Guidelines, e.g. “Don’t use colour without…” Principles, e.g. flexibility, recoverability

Engineering Users, Tasks, Machines, Performance. Highly specific advice

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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

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

Existing users and artefacts

Current task model

Envisioned taskmodel

User interfacedesign

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The Analysis-Design gulf

TA produces descriptions

The problem: How to use descriptions of user tasks to design systems

Descriptions Systemsgoals 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

Preparelectures

Visitstudents

Hold supervisionmeetings

Markassignments

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TKS: Objects

Describe users’ knowledge of objects in a domain

Items for sale

Audiobook BookMagazine

“Brighton Rock” “Noddy and the goblins”

“Human Computer

Interaction”

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TKS: Goals

Describe users’ knowledge of goals Hierarchy, control relations

Take a book order

Enter order details

Send order to publisher

Enter customer details

Enter book details

Get deposit

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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

ScrollSheet plot

Means

SIMSEQ

SEQDEP

SIM

CONTROL

TRIAL5TRIAL4TRIAL3TRIAL2TRIAL1

420

380

340

300

260

220

180

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Results: task errors

ScrollSheet plot

Means

SIMSEQ

SEQ

SIM

CONTROL

TRIAL5TRIAL4TRIAL3TRIAL2TRAIL1

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12

10

8

6

4

2

0

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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 -> TM -> GUI Operational Hmm? What objects? Rep?

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Unprincipled task model

Enter orderdetails

Enter cust.address

Enter bookprice

Enter cust.first name

Enter bookedition

Enter bookauthor

Enter bookISBN

Snd order topublisher

Take a book order

Taxonomic relation

a enables b

Subgoals not shownhere

a b

Key

Take depositof

Deposit paid . . .

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Unprincipled design

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Sequential dependency condition

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Principled task model

Deposittaken

Enter orderdetails

Enter customerdetails

Enter cust.address

Enter bookprice

Enter cust.first name

Enter bookedition

Enter cust.sec’nd name

Enter booktitle

Enter bookauthor

Enter bookISBN

Enter cust.tel. num.

Enter bookdetails

Send orderto publisher

Enter bookquantity

Get deposit

Take a book order

Total priceknown

Taxonomic relation

a enables b

Subgoals not shownhere

a b

Key

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Principled GUI