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Task Analysis. IACT 403 IACT 931 CSCI 324 Human Computer Interface Lecturer: Gene Awyzio Room: 3.117 Phone: 4221 4090 Email: [email protected] Overview. What is task analysis? Task Analysis Methods task decomposition knowledge based analysis entity-relationship techniques

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Task analysis l.jpg

Task Analysis

IACT 403 IACT 931 CSCI 324

Human Computer Interface

Lecturer: Gene Awyzio

Room: 3.117

Phone: 4221 4090

Email: [email protected]

Overview l.jpg

  • What is task analysis?

  • Task Analysis Methods

    • task decomposition

    • knowledge based analysis

    • entity-relationship techniques

  • Sources of Information

  • Uses of Task Analysis.

What is task analysis l.jpg
What is Task Analysis?

  • Methods of analysing people's jobs:

    • what people do

    • what things they work with

    • what they must know

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What is Task Analysis?

  • Example:

    • in order to clean the house

      • get the vacuum cleaner out

      • fix the appropriate attachment

      • 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

  • Task decomposition

    • splitting task into (ordered) subtasks

  • Knowledge based techniques

    • what the user knows about the task and how it is organised

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Approaches to task analysis

  • Entity-relation based analysis

    • relationships between objects and actions and the people who perform them

  • General method:

    • observe

      • unstructured lists of words and actions

    • organise

      • using notation or diagrams

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Differences from other techniques

  • Systems analysis

    • focus - system design

  • Task analysis

    • focus - the user

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Differences from other techniques

  • Cognitive models

    • focus - internal mental state

    • granularity - practiced `unit' task

  • Task analysis

    • focus - external actions

    • granularity - whole job

    • However

      • much overlap in general

      • differences have exceptions

Task decomposition l.jpg
Task Decomposition

  • Aims:

    • describe the actions people do

    • structure them within task subtask hierarchy

    • describe order of subtasks

  • Focus on Hierarchical Task Analysis (HTA)

    • It uses:

      • text and diagrams to show hierarchy

      • plans to describe order.

Textual hta description l.jpg
Textual HTA description

  • Hierarchy description …

    • 0. in order to clean the house

      • 1. get the vacuum cleaner out

      • 2. fix 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

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Textual HTA description

  • ... 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.

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Generating the hierarchy

  • get flat list of tasks

  • group tasks into higher level tasks

  • 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

  • Error cost: stop when P x C is small

  • Motor actions: lowest sensible level.

Diagrammatic hta l.jpg
Diagrammatic HTA

  • line under box means no further expansion.

  • Plans shown on diagram or written elsewhere.

  • Same information as:

    • 0. make a cup of tea

      • 1. boil water...

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Refining the description

  • Given initial HTA (textual or diagram)

    • How to check/improve it?

    • Some heuristics:

      • paired actions

        • e.g., where is `turn on gas’

      • restructure

        • e.g., generate task `make pot’

      • balance

        • e.g., is `pour tea' simpler than making pot?

      • Generalise

        • e.g., make one cup or two... or more.

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Types of plan

  • fixed sequence

    • e.g., 1.1 - 1.2 -1.3

  • optional tasks

    • e.g., if the pot is full 2

  • waiting for events

    • e.g., when kettle boils 1.4

  • cycles

    • plan 5

    • 5.2 empty cups? for each guest 5.3




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Types of plan

  • time-sharing

    • e.g., do 1; at the same time …

  • discretionary

    • e.g., do any of 3.1, 3.2 or 3.3 in any order

  • mixtures

    • most plans involve several of the above.

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Knowledge Based Analyses

  • Focus on:

    • Objects - used in task

    • Actions - performed

    • Taxonomies represent levels of abstraction

Knowledge based analyses19 l.jpg


motor controls

steering steering wheel, indicators



ignition, accelerator, foot brake


clutch, gear stick



headlights, hazard lights


courtesy light



front wipers, rear wipers


front washers, rear washers


temperature control, air direction, fan, rear screen heater


hand brake, door lock


numerous others

Knowledge Based Analyses

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TDH notation

  • TDH - Task Description Hierarchy

  • Three types of branch point in taxonomy:

    • XOR

      • normal taxonomy

      • object in one and only one branch

    • AND

      • object must be in both

      • represents multiple classifications

    • OR

      • weakest case

      • can be in one, many or none

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TDH notation

  • Example:

    • wash/wipe AND

      • function XOR

        • wipe

          • front wipers, rear wipers

        • wash

          • front washers, rear washers

      • position XOR

        • front

          • front wipers, front washers

        • rear

          • rear wipers, rear washers.

Larger tdh example l.jpg
Larger 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

More on tdh l.jpg
More on TDH

  • Uniqueness rule:

    • can the diagram distinguish all objects?

      • e.g., plate is:

        • kitchen item/shape( flat)/ function{preparation,dining(for food)}/

        • nothing else fits this description

More on tdh24 l.jpg
More on TDH

  • Actions have taxonomy too:

    • kitchen job OR

      • preparation

        • beating, mixing

      • cooking

        • frying, boiling, baking

      • dining

        • pouring, eating, drinking.

Abstraction and cuts l.jpg
Abstraction and cuts

  • After producing detailed taxonomy `cut' it to yield abstract view.

  • That is, ignore lower level nodes.

    • e.g., cutting above shape and below dining, plate becomes:

      • kitchen item/function {preparation,dining}/

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Abstraction and cuts

  • This is a term in

    • Knowledge Representation Grammar (KRG)

  • These can be more complex:

    • `beating in a mixing bowl' becomes

      • kitchen job(preparation)

        • using a kitchen item/ function {preparation}/.

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Entity-Relationship Based Techniques

  • Emphasis on objects, actions and their relationships

    • Similar to object-oriented analysis, but …

      • includes non-computer entities

      • emphasises domain understanding not implementation

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Entity-Relationship Based Techniques

  • 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.

Objects l.jpg

  • 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?

Objects30 l.jpg

  • Composite objects:

    • sets: the team = { Vera, Sam, Tony }

    • tuples: tractor may be < Fergie, plough >

  • 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

Actions l.jpg

  • 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)

Actions32 l.jpg

  • Note:

    • implicit agents - read behind the words

      • `the field was ploughed' - by whom?

    • indirect agency - the real agent?

      • `Vera programmed the controller to irrigate the field’

    • messages - a special sort of action

      • `Vera told Sam to …’

    • rôles - an agent acts in several rôles

      • Vera as worker or as manager.

E r example i objects and actions l.jpg
E/R Example I - objects and actions

  • Object Sam human actor

    • Actions:

      • S1: drive tractor

      • S2: dig the carrots

  • Object Vera human actor - the proprietor

    • Actions: as worker

      • V1: plant marrow seed

      • V2: program irrigation controller

    • Actions: as manager

      • V3: tell Sam to dig the carrots

  • Object the men composite

    • Comprises: {Sam, Tony}

E r example i objects and actions34 l.jpg
E/R Example I - objects and actions

  • Object glasshouse simple

    • Attribute:

      • humidity: 0-100%

  • Object Irrigation Controller non-human actor

    • Actions:

      • IC1: turn on Pump1

      • IC2: turn on Pump2

      • IC3: turn on Pump3

  • Object Marrow simple

    • Actions:

      • M1: germinate

      • M2: grow.

Events l.jpg

  • Events are 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 ...'

Relationships l.jpg

  • object - object

    • social - Sam is subordinate to Vera

    • spatial - pump 3 is in the glasshouse

  • action - object

    • agent - (listed with object)

    • patient and instrument

Relationships37 l.jpg

  • actions and events

    • temporal and causal

      • `Sam digs the carrots because Vera told him’

  • Temporal relations

    • also use HTA or dialogue notations.

    • show task sequence (normal HTA)

    • show object lifecycle (see page 241).

E r example ii events and relations l.jpg
E/R example II - events and relations

  • Events

    • Ev1: humidity drops below 25%

    • Ev2: midnight

  • Relations: object - object

    • location ( Pump3, glasshouse )

    • location ( Pump1, Parker's Patch )

E r example ii events and relations39 l.jpg
E/R example II - events and relations

  • Relations: action - object

    • patient ( V3, Sam )

      • Vera tells Sam to dig

    • patient ( S2, the carrots )

      • Sam digs the carrots …

    • instrument ( S2, spade )

      • … with the spade

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E/R example II - events and relations

  • Relations: action - event

    • before ( V1, M1 )

      • the marrow must be sown before it can germinate

    • triggers ( Ev1, IC3 )

      • when humidity drops below 25%, the controller turns on pump 3

    • causes ( V2, IC1 )

    • the controller turns on the pump because Vera programmed it.

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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 (see Chapter 11)

  • Interviews

    • the expert: manager or worker? (ask both!).

Early analysis l.jpg
Early analysis

  • Extraction from transcripts

    • list nouns (objects) and verbs(actions)

    • beware technical language and context

      • `the rain poured’

      • `I poured the tea’

  • Sorting and classifying

    • grouping or arranging words on cards

    • ranking objects/actions for task relevance (see Ch. 11)

    • use commercial outliner

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Early analysis

  • Iterative process:

    • data sources  analysis

  • But costly, so use cheap sources where available.

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Manuals and Documentation

Procedural `how to do it' manual

from HTA description

useful for extreme novices

or when domain too difficult

assumes all tasks known

Conceptual manual

from knowledge or entity/relation based analyses

good for open ended tasks

Example: tea making manual from HTA

Uses of Task Analysis I

To make cups of tea

boil water - see page 2empty potmake pot - see page 3wait 4 or 5 minutespour tea - see page 4

-page 1-

Make pot of teaonce water has boiledwarm potput tea leaves in potpour in boiling water

-page 3-

Uses of task analysis ii l.jpg
Uses of Task Analysis II

  • Requirements capture and systems design

    • lifts focus from system to use

    • suggests candidates for automation

    • uncovers user's conceptual model

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Uses of Task Analysis II

  • Detailed interface design

    • taxonomies suggest menu layout

    • object/action lists suggest interface objects

    • task frequency guides default choices

    • existing task sequences guide dialogue design

  • NOTE.

    • task analysis is never complete

    • rigid task based design  inflexible system

Questionnaires l.jpg

  • Set of fixed questions given to users.

  • Advantages:

    • quick and reaches large user group

    • can be analysed more rigorously

  • Disadvantages

    • less Flexible

    • less probing

  • Need careful design

    • what information is required?

    • how are answers to be analysed?

Question types l.jpg
Question Types

  • Dichotomous

  • Multiple Choice

  • Multiple Response

  • Open Ended

  • Rank/Match

  • Likert

  • Semantic Differential

  • Rating

Dichotomous l.jpg

  • These are designed to be answered yes or no. The respondent should have the opportunity to answer "I don't know" or "I don't remember".

  • e.g. Do you use sampling in your production process?

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  • Advantages of dichotomous questions:

    • easy to ask

    • easy to understand

    • quick to ask

    • quick/easy to record

    • easy to analyse

  • Disadvantage

    • misunderstandings are possible as shades of meaning are not incorporated to derive detailed information, a large number of such questions would need to be asked

Multiple choice l.jpg
Multiple Choice

  • Multiple-choice questions permit only one answer. By convention, radio-buttons are used on computer screens where only one option is allowed. Respondent should also be able to answer "I don't know".

  • e.g. How would you rate the programme?

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Multiple Choice

  • Advantages of multiple-choice questions:

    • allow many shades of meaning in answers

    • give respondent freedom of choice

    • easily recorded

    • easy to analyse

  • Disadvantages

    • difficult to ensure list of answers is complete

    • difficult to phrase initially exclusive answers

    • the list of answers should not be too long

Multiple response l.jpg

Multiple-response questions can have two or more answers.

By convention, check-boxes are used on computer screens where several options are allowed.

Respondent should also be able to answer "I don't know", "all" or "none".

Questions can have any number of responses or a fixed number as illustrated below.

e.g. Which three of the following best describe the show?

Multiple Response

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Multiple Response

  • Advantages of multiple-response questions

    • allow many shades of meaning in answers

    • give respondent freedom of choice

    • easily recorded

    • easy to analyse

  • Disadvantages

    • difficult to ensure list of answers is complete

    • difficult to phrase initially exclusive answers

    • the list of answers should not be too long

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Open Ended

  • Designedto give respondent complete freedom of choice in answering and thus derive maximum information.

  • Often used where there is insufficient information available on a topic to permit complete lists of alternative answers.

  • Difficult to analyse with computers.

    • e.g. How enjoyable did you find the presentation?

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Open Ended

  • Some structure can be added using the following techniques:

  • Word association

    • Words are presented, and respondents note the first word that comes to mind.

    • e.g. What is the first word that comes to your mind when you see the following?

      • Your mother

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Open Ended

  • Sentence completion

    • Incomplete sentences are presented, and respondents complete them.

    • e.g. When I choose a beer, the most important consideration in my decision is

Open ended58 l.jpg
Open Ended

  • Advantages of open-ended questions

    • produce extensive information

    • responses are free from bias of suggested answers

    • many facets of respondent's behaviour revealed

  • Disadvantages

    • can require slow verbatim recording

    • interviewers tend to select information they believe significant

    • lengthy interviews

    • difficult to analyse

    • many incoherent answers

    • much irrelevant information received

    • analysis requires groupings of answers - which loses much of the shades of meanings

Rank match l.jpg

  • e.g. Rank the following factors in order of importance when you buy a car

After sales support

Brand name

Value for money

Fuel economy


Other (please specify)

Likert l.jpg

  • Likert questions are statements with which the respondent indicates the amount of agreement/ disagreement.

    • e.g. Small shops generally give better service than large ones

Semantic differential l.jpg



Semantic Differential

  • In this type of question a scale is inscribed between two bipolar words, and the respondent selects the point that represents the direction and intensity of his or her feelings.

  • e.g. How would you describe your views on shops opening on Sundays?

Question sequence l.jpg
Question Sequence

  • There are a number of general rules which should be considered when the order of the questions is arranged.

  • Those questions which are easy to answer should be put at the beginning, in order to give the respondent confidence in his ability to help you.

  • Those questions which are likely to interest the respondent should be early in the order.

  • The questions should be asked in a logical order.

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Question Sequence

  • Filter questions should follow each other without being interrupted by other questions.

  • Before a change of topic, introductory phrases should be used to enable the respondent to make an easy transition.

  • Personal or emotional questions should be at the end.

  • More complicated questions should be at the end.

  • These guidelines tend to imply recommendation of a funnel design: