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.
2.
3.
4.
5.
Get the vacuum cleaner out
Fix the attachment
Clean the rooms
When the dust bag gets full, empty it
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:
Which looks at the way a task is split into subtasks, and the order in which these
are preformed
 Knowledge-based 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:
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 form 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. 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
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
STOPPING RULES
 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.
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.
0.
4.
3.2.
5.
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
HTA EXAMPLE
 To better explain
what is being
talked about,
here is a video of
how to use
hierarchal task
analysis to set a
table.
TYPES OF PLANS
 fixed sequence
-
1.1 then 1.2 then 1.3
 optional tasks
-
if the pot is full 2
 wait for events
- when kettle boils 1.4
 cycles
-
do 5.1 5.2 while there are still empty cups
 time-sharing
-
do 1; at the same time ...
 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.
 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.
 Class Participation:
 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:
 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
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 – BASED TECHNIQUES
 Entity –
relationship
modeling is an
analysis
technique usually
associated with
database design
and more recently
object-oriented
programming.
OBJECTS
 Start with list of objects and classify them:
 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:
Example: Irrigation Pump
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)
 Performed by the agent (someone or something)
 There can be other attributes associated with an action
These are known as instruments
 Example: “the gardener dug the soil with the spade”
Patient: Soil
Agent: Gardener
Instrument: Spade
EVENTS
 Anything which happens
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
 Object-Object
Irrigation pump 3 is situated in the glasshouse
 Action-Object
Vera tells Sam to dig the carrots with the spade
ATOM METHOD
 Analysis for Task Object Modeling (ATOM)
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
 Observation
 Interviews
 Initial Analysis
 Sorting and Classification
USES OF TASK ANALYSIS
 Manuals and Tuition
 Requirements Capture and Systems Design
 Detailed Interface Deisgn
SUMMARY
 There are several task analysis
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
 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: http://www.hcibook.com/e3/scenario/phone
 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