Transcript HCI Lecture 23 Task analysis.ppt

Lecture 23
Task analysis
Today’s Outline

Today we will cover
 Introduction to Task
 Task Analysis
 Types of Task Analysis
 Documentation and User Manuals
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Introduction


What are Tasks
 What the user has to do (or thinks what he/she has to do) in order
to accomplish a goal
 Each task should be
 Meaningful
 Associated with a goal
 Identifiable by the user
What is Task Analysis
 A process of analyzing the way people perform their tasks
 The things they do
 The things they act on
 The things they need to know
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What is a task?

Skehan (1996)
A task is ‘an activity in which: meaning is primary; there
is some sort of relationship to the real world; task
completion has some priority; and the assessment of
task performance is in terms of task outcome’.
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What is a task?
 Nunan (1989)
A communicative task is ‘a piece of classroom work
which
involves
learners
in
comprehending,
manipulating, producing, or interacting in the target
language while their attention is principally focused on
meaning rather than on form. The task should also
have a sense of completeness, being able to stand
alone as a communicative act in its own right
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Examples of tasks
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Borrowing a library book
Making an airline reservation
Writing a cheque
Opening a bank account
Post a letter in the post-office
Six criterial features of a task (Ellis, 2003: 9-10)
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A task is a workplan.
A task involves a primary focus on meaning.
A task involves real-world processes of
language use.
A task can involve any of the four language
skills.
A task engages cognitive processes.
A task has clearly defined communicative
outcome.
Task Analysis

fundamental methodology in the assessment and reduction of
human error

Nearly all task analysis techniques provide, as a minimum, a
description of the observable aspects of operator behavior at
various levels of detail, together with some indications of the
structure of the task - action oriented approaches.

Other techniques focus on the mental processes which underlie
observable behavior, e.g. decision making and problem solving
- cognitive approaches
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Task Analysis

What: Analysis of a task in terms of it cognitive, motor, and
perceptual aspects.

Why:
– To understand how people work.
– To systematically examine the tasks that a user will perform
on a new or existing system.
– Task analysis for a new system forms the basis of the design
for user interaction.

How: Using a variety of data collection methods and task
description techniques.
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What is TA?
Methods to analyze people's jobs:
 what
people do
 what
things they work with
 what
they must know
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Goals of Task Analysis

Elicit descriptions of what people do

Represent those descriptions

Predict difficulties, performance

Measure learnability, transfer of knowledge between systems

Evaluate systems against usability and/or functional
requirements
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An Example
For example, if we were considering the job of housekeeping, we would want
to say things like:
To clean the house
• Get the vacuum cleaner out
• Fix the appropriate attachments
• Clean the rooms
• When the dust bag gets full, empty it
• Put the vacuum cleaner and tools away
Must know about:
• vacuum cleaners, their attachments, dust bags, cupboards, rooms, etc.
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Approaches to Task Analysis

1.
2.
3.

Three different approaches are,
Task Decomposition
Knowledge Based Techniques
Entity Relation Based Analysis
Helps in
 Training materials and documentation
 The statement of requirements of this system
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General Method

observe

collect unstructured lists of words and actions

organize using notation or diagrams
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Differences from other techniques
Systems analysis
vs.
Task analysis
system design - focus - the user
Cognitive models
vs.
Task analysis
internal mental state - focus - external actions
practiced `unit' task - focus - whole job
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Task Decomposition


What is Task Decomposition
 A top-down process in which a task is split into subtasks by
sequence
Aims
 Describe the actions users do
 Structure actions in a task-subtask hierarchy
 Describe order of subtasks
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HTA

Hierarchical Task Analysis is a systematic method of describing
how work is organized in order to meet the overall objective of
the job.

It involves identifying in a top down fashion the overall goal of
the task, then the various sub-tasks and the conditions under
which they should be carried out to achieve that goal.

complex planning tasks can be represented as a hierarchy of
operations - different things that people must do within a
system and plans - the conditions which are necessary to
undertake these operations.
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Hierarchical Task Analysis






One of the most common task analysis techniques
Recursively break task down into subtasks
Describes task in terms of:
 goals
 operations
 Plans
Goals (what person is seeking to achieve)
Operations (activities to meet goals)
Plans (conditions under which operations are carried out)
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0. Clean the house
1. Get the vacuum cleaner out
2. Get the appropriate attachment
3. Clean the rooms
3.1. Clean the hall
3.2. Clean the living rooms
3.3. Clean the bedrooms
4. Empty the dust bag
5. Put vacuum cleaner and attachments away
Plans
Plan 0: do 1 - 2 - 3 - 5 in that order. When the dust bag gets full do 4
Plan 3: do any of 3.1, 3.2 or 3.3 in any order depending on which rooms need cleaning
Textual HTA of the Task of Cleaning a House
• Indentation is used to denote the levels in the task hierarchy
• Plans are labeled by the tasks they correspond to
• Only the plans denote the order of task performance
• Not all subtasks need to performed, and not necessarily in the order presented in the hierarchy
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0.
Clean the house
Plan 0: do 1 - 2 - 3 - 5 in that order.
when the dust bag gets full do 4
1.
Get the vacuum
cleaner out
2.
Fix the appropriate
attachment
3.1.
Clean the
hall
3.
4.
5.
Clean the
Empty the
Put vacuum cleaner
rooms
dust bag
and attachments away
Plan 3: do any of 3.1, 3.2 or 3.3 in any
order depending on which rooms need
cleaning
3.2
Clean the
living room
3.3.
Clean the
bedrooms
Diagrammatic HTA of the Task of Cleaning a House
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Generating Hierarchy


Identify the Major Task to be Analyzed
 e.g. clean house, purchase a flight ticket online, copy
a ten-page paper, etc.
Break Down the Major Task into Subtasks
 What subtasks must be accomplished in order to
perform the main task
 Refer to various sources (e.g. direct observation,
expert opinion, documentation, etc.)
 Try to be specific in terms of the objectives of subtasks
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Generating Hierarchy …



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Decide Upon the Level of Detail into Which to Further
Decompose the Subtasks
 Some stopping rule
Continue the Decomposition Process
 Keep decompositions and numbering consistent
Group Some Subtasks (If Too Detailed) into Higher-Level
Subtasks
Present the Hierarchy to a Domain Expert to Check for Errors or
Omissions
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Stopping Rule

Depends on the Purpose of the Task Analysis
 Put more effort into those subtasks which are directly relevant to
the intended purpose
0. In an emergency situation in a chemical plant
1. Read the alarms
2. Work out appropriate corrective action
3. Perform corrective action
• If our ultimate aim is to install computer monitoring of the plant, then
we would be interested in expanding subtasks 1 and 3
• If the aim is to produce online operations manuals, then subtask 2
would require expansion
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Stopping Rule


P × C Rule
 Particularly appropriate when the aim is to design training
materials
 If the probability of making a mistake in task (P) multiplied by the
cost of the mistake (C) is below a threshold, then stop expanding
 Simple tasks need not to be expanded unless they are critical
Stop at the point where the task contains purely muscle actions or
involves purely cognitive activities
 e.g. mouse movement, recall someone’s name
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HTA of the Task of Making a Cup of Tea
0.
Make a cup of tea
Plan 0:
do 1
At the same time, if the pot is full, do 2
Then do 3 – 4
After four or five minutes do 6
1.
Boil water
2.
Empty pot
3.
Put tea
leaves in pot
4.
Pour in
boiling water
5.
Wait for 4 or
5 minutes
6.
Pour tea
Plan 1:
do 1.1 – 1.2 – 1.3
when kettle boils, do 1.4
1.1.
Fill kettle
1.2
Put kettle
on stove
1.3.
Wait for
kettle to boil
1.4.
Turn
off gas
Any omission or error?
Can some first-level subtasks be combined ?
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0.
make a cup of tea
Plan 0:
do 1
At the same time, if the pot is full, do 2
Then do 3 – 4
After four or five minutes do 5
1.
Boil water
2.
Empty pot
3.1.
Warm pot
4.
3.
5.
Wait for 4 or
Make pot
Pour tea
5 minutes
of tea
Plan 3:
do 3.1 – 3.2 – 3.3
Can we expand 5?
3.2.
3.2.
Pour in
Put tea
leaves in pot boiling water
Plan 1:
do 1.1 – 1.2 – 1.3 – 1.4
when kettle boils, do 1.5
1.1.
Fill kettle
1.2
Put kettle
on stove
1.3.
Turn
on gas
1.4.
Wait for
kettle to boil
1.5.
Turn
off gas
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Suppose subtask 5 “Pour tea” can be further decomposed
5. Pour tea
5.1. put milk in cup
5.2. fill cup with tea
5.3. add sugar to taste
Plan 5.
Do 5.1 – 5.2 – 5.3
What if we want to make more than one cup?
5.1
5.2
5.3
More cup(s)?
Yes
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0.
make cups of tea
Plan 0:
do 1
At the same time, if the pot is full, do 2
Then do 3 – 4
After 4 or 5 minutes do 6
1.
Boil water
2.
Empty pot
4.
Wait for 4 or
5 minutes
3.
Make pot
Plan 3:
do 3.1 – 3.2 – 3.3
3.1.
Warm pot
3.2.
Put tea
leaves in pot
Plan 1:
do 1.1 – 1.2 – 1.3 – 1.4
when kettle boils, do 1.5
1.1.
Fill kettle
1.2
Put kettle
on stove
1.3.
Turn
on gas
3.2.
Pour in
boiling water
1.4.
Wait for
kettle to boil
5.
Pour tea
Plan 5:
5.1 5.2 5.3 More cup(s)?
Yes
5.2.
5.3.
5.1.
Add
Put milk Fill up
with tea sugar
in cup
1.5.
Turn
off gas
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Handling Waiting
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
Redundant?
Plan or subtask?

Considered as a subtask if it is a
“busy” waiting
 e.g. The person may be chatting
while the tea brews
Included in the plan if time seems
critical for the task sequence
Perhaps a little redundant in this
example, but task analysis is not an
exact science
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Types of Plan


Fixed Sequence
 The same sequence of subtasks is always followed
 e.g. Plan 3 in the HTA of tea making
Optional Subtasks
 Subtasks
that may or may not be performed depending on
circumstances
 e.g.
Subtask 2 in plan 0 in the HTA of tea making
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Types of Plan

Waiting-For Events
 Wait for a certain time
 e.g. Wait for 4 or 5 minutes in plan 0 in the
HTA of tea making
 Wait for the occurrence of some event
 e.g. Wait for kettle to boil in plan 1 in the
HTA of tea making
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Types of Plan


Cycles
 Repeat some subtasks until a condition is reached
 e.g. Repeatedly perform subtasks 5.1 – 5.3 until no more
cup is left in the HTA of tea making
Time Sharing
 Some subtasks can be done at the same time
 e.g. Subtasks 1 and 2 can be done at the same time in the
HTA of tea making
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Types of Plan …


Discretionary Subtasks
 Whether to perform some subtasks is at the people’s
discretion
 e.g. In plan 3 in the HTA of room cleaning, the person is
allowed to clean any room that he/she thinks needs
cleaning and in any order
Mixtures
 Most plans are a mixture of different types
 e.g. Plan 1 in the HTA of tea making is largely a fixed
sequence but split by a wait
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HTA

Advantages
 HTA is a simple and flexible method that does not depend
on a methodological context.
 HTA
enables the representation of a task hierarchy that
could be further detailed.
 Although
HTA is task oriented and to some extent user
oriented it still maintains a strong relationship with
traditional software engineering.
 HTA
provides information, inefficiencies in tasks, that can
be used for developing product requirements.
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HTA

Disadvantages
 There are no strict rules for creating an HTA diagram so different
analysts will generate inconsistent hierarchies at varying levels of
detail.

HTA requires both training and experience. It is not a tool that can
be applied immediately.


HTA is not a predictive tool. It focuses on existing tasks.
HTA diagrams can become quite complex

Concurrent tasks and tasks that overlap cannot be described

Interruption hard to express in diagrams
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Knowledge-Based Analysis

Understand the knowledge needed to perform a task:
 list all objects and actions involved
 build taxonomies to structure these
 use this understanding for training
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Knowledge-Based Analysis

Need to know about: car control classification
 steering  steering wheel, indicators
 engine/speed
 direct
 ignition, accelerator, foot brake
 gearing
 clutch, gear stick
 lights
 external
 headlights, hazard lights
 internal
 courtesy light
 parking  hand brake, door lock
 etc.
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Knowledge-Based Analysis

Taxonomy:
 different structures might be possible, depending on intended
purpose and audience
 e.g.,
 driving versus repairing by mechanic
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Knowledge-Based Analysis

Task descriptive hierarchy:
 XOR |
 object in only one category
 AND /
 object in all categories
 OR {
 object in at least one category
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Knowledge-Based Analysis

car controls XOR
…
 wash/wipe AND
 function XOR
 wipe
 wash
 position XOR
 front
 rear
…
 front wipers, rear wipers
 front washers, rear washers
 front wipers, front washers
 rear wipers, rear washers
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Knowledge-Based Analysis

kitchen item OR
 preparation
 mixing bowl, plate,
chopping board
 cooking  frying pan, casserole,
saucepan
 dining
 plate, soup bowl,
casserole, glass
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Knowledge-Based Analysis

Uniqueness rule:
 must be able to distinguish any two specific objects
 e.g.,
 cannot distinguish mixing bowl and chopping board
 can distinguish mixing bowl and plate
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Knowledge-Based Analysis

kitchen item AND
 / shape XOR
 | dished
 mixing bowl, casserole,
saucepan, soup bowl, glass

/
| flat
 plate, chopping board,
frying pan
function OR
 …
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Knowledge-Based Analysis

kitchen item AND
 / shape XOR
 …
 / function OR
 { preparation

{ cooking

{ dining XOR
 | for food
 | for drink
 mixing bowl, plate,
chopping board
 frying pan, casserole,
saucepan
 plate, soup bowl, casserole
 glass
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Knowledge-Based Analysis

Unique path:
 each object can be represented by a knowledge
representation grammar (KRG) term
 e.g.,
 a casserole dish
 kitchen item/shape(dished)/
function{cooking,dining(for food)}/
 kitchen item whose shape is dished AND its function is
cooking OR dining for food
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Knowledge-Based Analysis

Taxonomy of actions:
 can also structure actions, based on genericity instead of a
“how to do it” decomposition
 make general statements about tasks
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Knowledge-Based Analysis

kitchen job OR
 { preparation
 beating, mixing, pouring
 { cooking
 frying, boiling, baking
 { dining  pouring, eating, drinking
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Knowledge-Based Analysis

Taxonomies of objects and actions
 crosscheck to look for omissions
 perhaps easier to see what people use than to see what they
do
 add taxonomies
 e.g., classify foods
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Knowledge-Based Analysis

Generic descriptions of simple tasks:
 KRG sentence
 e.g.,
 eating a carrot off a plate
 kitchen job(dining)
using a kitchen item
/shape(flat)/function{dining,preparation}/
to food(root vegetable)
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Knowledge-Based Analysis

Issues:
 generification
 not bothering with certain low-level distinctions
 too many different KRG sentences
 perhaps more generification needed
 too few different KRG sentences
 level of abstraction too great
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Entity-Relationship Techniques
Focus on objects, actions and their relationships
Similar to OO analysis, but …


includes non-computer entities
emphasises domain understanding not implementation
Running example
‘Vera's Veggies’ – a market gardening firm
owner/manager: Vera Bradshaw
employees: Sam Gummage and Tony Peagreen
various tools including a tractor `Fergie‘
two fields and a glasshouse
new computer controlled irrigation system
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Objects
Start with list of objects and classify them:
Concrete objects:
simple things: spade, plough, glasshouse
Actors:
human actors: Vera, Sam, Tony, the customers
what about the irrigation controller?
Composite objects:
sets: the team = Vera, Sam, Tony
tuples: tractor may be < Fergie, plough >
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Attributes
To the objects add attributes:
Object Pump3 simple – irrigation pump
Attributes:
status: on/off/faulty
capacity: 100 litres/minute
N.B. need not be computationally complete
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Actions
List actions and associate with each:
agent – who performs the actions
patient – which is changed by the action
instrument – used to perform action
examples:
Sam (agent) planted (action) the leeks (patient)
Tony dug the field with the spade (instrument)
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Events
… when something happens

performance of action
‘Sam dug the carrots’

spontaneous events
‘the marrow seed germinated’
‘the humidity drops below 25%’

timed events
‘at midnight the controller turns on’
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Relationships

object-object
social - Sam is subordinate to Vera
spatial - pump 3 is in the glasshouse

action-object
agent (listed with object)
patient and instrument

actions and events
temporal and causal
‘Sam digs the carrots because Vera told him’

temporal relations
use HTA or dialogue notations.
show task sequence (normal HTA)
show object lifecycle
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Relational Model Representation
Object
Employee
Relationship
Works on
Object
Project
Entity Relationship Diagram is used to conceptually represent
Relational database.
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Sources of Information
Documentation

N.B. manuals say what is supposed to happen
but, good for key words and prompting interviews
Observation

formal/informal, laboratory/field
Interviews

the expert: manager or worker? (ask both!)
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Early analysis
Extraction from transcripts


list nouns (objects) and verbs (actions)
beware technical language and context:
`the rain poured’ vs. `I poured the tea’
Sorting and classifying



grouping or arranging words on cards
ranking objects/actions for task relevance (see ch. 9)
use commercial outliner
Iterative process:
…
data sources  analysis
but costly, so use cheap sources where available
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Uses – manuals & documentation
Conceptual Manual

from knowledge or entity–relations based analysis

good for open ended tasks
Procedural ‘How to do it’ Manual

from HTA description
 good for novices
 assumes all tasks known
To make cups of tea
Make pot of tea
once water has boiled
boil water –– see page 2
empty pot
make pot –– see page 3
wait 4 or 5 minutes
pour tea –– see page 4
–– page 1 ––
warm pot
put tea leaves in pot
pour in boiling water
–– page 3 ––
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Summary

We have covered today different aspects of task analysis
including
 What is task analysis?
 HTA
 Knowledge Based Task Analysis
 Entity Relationship Task Analysis
 Documentation
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