Chapter 15 – Task Analysis - USC Upstate: Faculty

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INTRODUCTION

What is task analysis?


Is the process of analyzing the way people preform the jobs: the things they do ,
the things, they act on, and the things they need to know.


Example:


In order to clean the house:

1.
Get the vacuum cleaner out

2.
Fix the attachment

3.
Clean the rooms

4.
When the dust bag gets full, empty it

5.
Put the vacuum cleaner and tools away


DIFFERENCES BETWEEN TASK ANALYSIS AND
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



THREE APPROACHES TO TASK ANALYSIS


Task decomposition:

¾
Which looks at the way a task is split into subtasks, and the order in which these
are preformed


Knowledge
-
b
ased techniques:


Which look at what the users need to know about the objects and actions
involved in a task and how that knowledge is organized


Entity
-
relation
-
based analysis:

¾
Which is an object
-
based approach where the emphasis is on identifying the
actors and objects, the relationships between them and the actions they
preform.

TASK DECOMPOSITION


Most task analysis techniques involve some
f
orm of task decomposition to
express this sort of behavior.


Aims:


describe
the actions people
do


structure
them within task subtask

hierarchy


describe
order of
subtasks


Variants:


Hierarchical
Task Analysis (
HTA)


most
common


Collaborative Task Tree (CTT)
(CNUCE,
Pisa)


uses
LOTOS temporal operators


TEXTBOOK EXAMPLE

Hierarchy description ...


0
. in order to 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


... and plans


Plan 0: do 1
-

2
-

3
-

5 in that order.

W
hen
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


N.B. only the plans denote order


HOW TO GENERATE A HIERARCHY

1. Get
list of tasks

2
. Group
tasks into higher level tasks

3
. Decompose
lowest level tasks further




How
do we know
when to
stop?


Is
“empty the dust bag”
simple
enough?


Purpose
: expand only
relevant
tasks


Motor
actions: lowest
sensible level



P x C Rule


Says that the probability of
making a mistake in the
task is (p) times the cost of
the mistake (
C
) is below a
threshold, then stop
expanding.

STOPPING RULES

HTA PARSING
SCENARIO

get out cleaner

fix carpet head

clean dinning room

clean main bedroom

empty
dustbag

clean sitting room

put cleaner away

1.

2.

3.2.

3.3.

3.2.

3.

4.

5.

0.

0. in order to 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


To better explain
what is being
talked about,
here is a video of
how to use
hierarchal task
analysis to set a
table.

HTA EXAMPLE

TYPES OF PLANS


fixed sequence

-

1.1 then 1.2 then 1.3

¾
optional tasks

-

if the pot is full 2

¾
wait for events

-

when kettle boils 1.4

¾
cycles

-

do 5.1 5.2 while there are still empty cups

¾
time
-
sharing

-

do 1; at the same time ...

¾
discretionary

-

do any of 3.1, 3.2 or 3.3 in any order


mixtures

-

most plans involve several of the above

KNOWLEDGE

BASED ANALYSIS


Begins by listing all the objects and actions involved in the task and then building
taxonomies (think about descriptions in biology) of them.

¾
The aim is to understand the knowledge needed to preform a task and thus to
help in the production of teaching materials and in assessing the amount of
common knowledge between tasks.


¾
Class Participation:

¾
What would be considered an example of an everyday taxonomy?


KNOWLEDGE
-
BASED ANALYSIS EXAMPLE

motor controls


steering
steering

wheel, indicators


engine/speed



direct
ignition, accelerator, foot brake



gearing
clutch, gear stick


lights



external
headlights, hazard lights



internal
courtesy light


wash/wipe



wipers
front wipers, rear wipers



washers
front washers, rear washers


heating
temperature control, air direction,


fan, rear screen heater


parking
hand brake, door lock


radio
numerous!


TASK DESCRIPTION
HIERARCHY (TDH)


Three types of branch point in taxonomy:

¾
XOR



normal taxonomy



object
in one and only one
branch


AND



object must be in both



multiple
classifications


OR



weakest case



can
be in one, many or none


ANOTHER TDH EXAMPLE

kitchen item AND

/____shape XOR

/ |____dished mixing bowl, casserole, saucepan,

/ | soup bowl, glass

/ |____flat plate, chopping board, frying pan

/____function OR


{____preparation mixing bowl, plate, chopping board


{____cooking frying pan, casserole, saucepan


{____dining XOR


|____for food plate, soup bowl, casserole


|____for drink
glass


NOTE:
‘/|{’ used for branch types.



ABSTRACTIONS AND CUTS


After producing detailed
taxonomy, we can use these in order to produce generic
descriptions of tasks

¾
That
is, ‘cut’ to yield abstract view


This
is
Knowledge Representation Grammar (KRG
)


KRG terms opt for a generic description or generification.


One example is to break down a tree and make note to how many times a
specific word is mentioned or used. If the number of occurrences is low,
then one does not bother with the lower
-
level distinctions.



The choice of an appropriate level to “cut” the tree is also influence by the
number of different sentences we get for a task.


If there are many, many sentences, we need to use generification.


Although if there are too few sentences, the level of abstraction is too great and
needs to be revaluated.


Entity


relationship
modeling
is an
analysis
technique usually
associated with
database design
and more recently
object
-
oriented
programming.

ENTITY


RELATIONSHIP


BASED TECHNIQUES

OBJECTS


Start with list of objects and classify them:


¾
Concrete
objects (specifies):


simple
things: spade, plough, glasshouse



Actors:


human
actors
:
Vera, Sam, Tony, the customers



Composite
objects (abstract):


sets
:
the team = Vera, Sam,
Tony


tuples
:
tractor may be <
Fergie

(the tractor),
plough >


ATTRIBUTES


To the
objects,
add attributes:


¾
Example:
I
rrigation
P
ump


Attributes:


status
: on/off/faulty


capacity
: 100
litres/minute



Example: TVs


Attributes:


Status: On/Off/Stand By


Type: Low Def./ High Def./Smart TV


ACTIONS


Actions change the patient (the state of something)

¾
Performed by the agent (someone or something)

¾
There can be other attributes associated with an action

¾
These are known as instruments




Example: “the gardener dug the soil with the spade”

¾
Patient: Soil


Agent: Gardener


Instrument: Spade


EVENTS


Anything which happens

¾
Actions performed are always events


Can also encounter spontaneous events


Example: The germination of a marrow seed


No agent is performing the germination


Some spontaneous events have no associated object at all


Example: Temperature changes


Events are also timed


Example: “At midnight”

RELATIONSHIPS


Tie objects, actions, and events together


¾
Object
-
Object

¾
Irrigation pump 3 is situated in the glasshouse


Action
-
Object

¾
Vera tells Sam to dig the carrots with the spade

ATOM METHOD


Analysis for Task Object Modeling (ATOM)

¾
Can be done in two ways


Analyze the order of subtasks and actions annotated by the objects involved


Refer to page 529


Can produce for any particular object a “life cycle” diagram representing all
the actions in which it participates


Refer to page 530


Most methods include some notion of class or inheritance hierarchy

SOURCES OF INFORMATION AND DATA
COLLECTION


Documentation

¾
Observation

¾
Interviews

¾
Initial Analysis

¾
Sorting and Classification


USES OF TASK ANALYSIS


Manuals and Tuition

¾
Requirements Capture and Systems Design

¾
Detailed Interface
Deisgn

SUMMARY


There are several task analysis

¾
Hierarchical task analysis decomposes a task into subtasks


Can be recorded either in a textual outline format or in a tree diagram


Knowledge based techniques built taxonomies of the objects used during a task
and the actions performed upon them


Information for task analysis can be drawn from different sources

¾
Analysis can be used to train and provide instruction


EXERCISE 15.6


This exercise is based on the mobile phone exercise on the book
site:
www.hcibooks.com


A user interface designer analyzes Andy’s behavior with his original
phone and realizes that both scenarios A and B are part of a general
pattern, as shown in the hierarchical task analysis (HTA) in Figure
15.8.

1.
Complete the HTA for phoning using the original phone taking
into account scenarios A and B only briefly describe your
solution.

2.
Do a complete HTA for phoning using the new phone based on
scenario C.

3.
You will find that scenario C does not quiet fit into the general
pattern in Figure 15.8. Discuss whether the solutions to 1 and 2
can be modified to emphasize their common features and
whether this would clarify the over task description.

OUR ANSWER
-

QUESTION 1

OUR ANSWER (CONT.)


QUESTION 2 & 3

THE END