1 cs2341 lecture 5: task analysis robert stevens stevensr

1http://img.cs.man.ac.uk/stevens

CS2341

Lecture 5: Task Analysis

Robert Stevens

http://www.cs.man.ac.uk/~stevensr


Introduction

• The way people perform tasks with current systems: real world and virtual

• Decomposition of tasks into sub-tasks• Classification of tasks knowledge• Listing of objects used and actions performed• Methodology• TA and Activity Diagrams


Task Analysis Basics• Analysis of how people perform their jobs: the things they use, the

actions they take and the things they need to know• In order to clean a house:

– Find vacuum cleaner and tools – Clean rooms that need to be cleaned– Empty dustbag when full– Put cleaner and tools away

• Need to know about state of rooms, locations of tools, operation of tools, etc.

• Strictly, should not include why people perform tasks…• The observable things that users do, but why included at a shallow

level• About existing systems – production of training materials• Used for clarification of task organisation and knowledge when

designing a new system


Three Kinds of Task Analysis• Hierarchical task analysis: How tasks are split into

sub-tasks, their ordering and when they are performed

• Classification of Task Knowledge: What users need to know about a task and how that knowledge is organised

• Entity Relationship analysis: An object based approach, concentrating upon Actors and objects they use, the relationships between them and the actions performed

• Different emphases and intentions


Scope

• Scope of TA wide• As well as a system, it will include surrounding

objects, actions, actors and tasks• In word processing, will include maintaining printers,

using filing cabinets, reference material, etc.• Many of these will never be part of any system• Establishes contexts of use• In TA the user is central• Similar to Activity Diagrams


Hierarchical Task Analysis

• Decomposition of a task like “clean the house” into sub-tasks

• Those sub-tasks further decomposed• Form a task hierarchy• Gives ordering of tasks• Plans give further instructions: Choice, disjoint paths• Formed from the viewpoint of one Actor, but other

actors included in task names and plans• Activity Diagrams organise and emphasise differently


Cleaning a House

0. in order to clean the house1. 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 the vacuum cleaner and attachments away

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, 3.3 in any order, depending on which rooms need cleaning.


Hierarchical Task Analysis (HTA)

• Task Decomposition• Numbers indicate levels of task• Plans give extra information about tasks: Choice, concurrency,

order, etc.• Plan 3 describes tasks 3.1, 3.2, 3.3 and 3.4• Underlining decomposition ended• Need stop condition• Textual and diagrammatic forms


Cleaning a house (2)

• Plan 0 tells us “emptying bag” done at any point – the conditional is expressed at a higher level

• If we only noticed a full bag during cleaning, the task would within task 3

• Not all rooms need to be cleaned• Rooms may be cleaned in any order• Cleaning orientated; varnishing or washing floor would indicate

the hall to be done last• A more sophisticated plan 3 could indicate different routines


Stopping Rules

• When does one stop modelling?• Sending nerve signals and flexing muscles?• Catabolising glucose to provide energy?• The formation of petroleum that will make plastics?• Cost benefit analysis – what is the cost of modelling something?• If P(mistake) * Cost(mistake) < threshold, then don’t model• Avoid cognitive activities, muscle actions,…• But be aware of what you are modelling for• Number of mouse clicks can be important!


Making Tea

1. Boil water

2. Empty pot

3. Make pot

4. Wait 4 – 5 mins (brewing)

5. Pour tea• Plan 0: do 1; at same if pot dirty, do 2; after 1 do 3

and 4; then do 5.


Making Tea (1)

5.1 5.2emptycups?

for eachguest 5.3

NO

YES

Pouring a round of tea for n people


More About Making Tea

• Which tasks need to be expanded?• Emptying pot and brewing need no decomposition• “I fill the kettle, put it on the hob and when it is boiling I turn off

the gas”• No mention of turning gas on – look for symmetry of tasks• Are we talking of one cup of tea per person or an arbitrary

number?• Does our description of 5 (previously) fit into the general

scheme of making a pot of tea?


Plan 1 1.1 – 1.2 – 1.3 – 1.4 when kettle boils, 1.5

0.make cupsof tea

1.boilwater

2.emptypot

3.makepot

4.wait 4 or5 minutes

5.pour tea

5.1 put milk in cup

5.2 fill cupwith tea

5.3 do sugar

3.3 pour inboiling water

3.1 warm pot

3.2 put tea leaves in pot

1.1 fillKettle

1.2 put kettle on stove

1.3 turn on and light gas

1.4 wait for kettle to boil

1.5 turn offgas

5.3.1 ask guestabout sugar

5.3.2add sugarto taste

Plan 0. do 1 at the same time, if the pot is full 2 then 3-4 after 4/5 minutes do 5

Plan 3 3.1 – 3.2 – 3.3

Plan 5.3 5.3.1 – if wanted 5.3.2

5.1 5.2 emptycups?

for eachguest 5.3

NO

YES

Making Tea(2)


Making Tea (3)

• “Empty pot” could be part of “make pot”• However, 2 can be concurrent with 1, but 3 “make pot” depends

on 1• Similarly, 5 “pour tea” is dependent on 4 “wait 4 – 5 mins”• So, have these tasks at same level, despite differences in

granularity• What about “warming pot”?


Methodology

• Documentation is a cheap way of gathering tasks and objects• Beware – manuals etc. can mislead• Manuals etc. often give a perfect view, but can give initial view• Observation & interview techniques are important• It is like requirements gathering• Verbs and nouns give things and relationships• Like class diagram modelling• Use outliners to draw hierarchy• Card sorting can be used to build taxonomy• Use intermediate TA to show to expert to reveal more

information• An iterative process


Task Analysis & Activity Diagrams

• Task Analysis: Actions, actors and objects• Activity diagrams capture same notions….• … but different intentions• Events explicit, immutable order, no cycles in Activity

Diagrams • Activity diagrams less detail – a high level view• Could write Diagrams for finer granularities, but roles

of actors (swim-lanes) and how they interact a higher level, organisational aspect is emphasised


Activity Diagram for House Cleaning

empty dust bag

finding vacuum cleaner and tools

clean rooms

put vacuum cleaner and tools away

dust bag full

dust bag full

dust bag full

Signal Receipt


Activity Diagram for Cleaning Rooms

clean living room

clean kitchen

clean hall

clean bedroom


Uses of HTA

• Application requirements: Can use TA as starting point for system requirements

• N.B. TA scope is very wide, but shows what should be supported and describes how a task is currently performed

• Tutorials and manuals: gives chapters, sections etc. and their order. The document matches the task

• Dialogue design – e.g. Menus: The functions are grouped according to task and “good” terms are used for the labels


Tea Making Tutorial

• Section in a tea-making tutorial:1. Boiling the Water

2. Preparing the Pot

3. Making the Pot

4. Brewing the Tea

5. Pouring the Tea


PowerPoint Menus

• Menu Bar has a collection of task oriented groups (File, Edit, View, Window, etc.)

• File menu has file related tasks• Open dialogue models file opening task –

finding, naming, giving type, etc.


Summary

• Describing the current state of the world• Actors, actions and objects and their

involvement in a task• Decomposition of a task into sub-tasks• Tasks and their plans• Representation, and stopping rules• Requirements, manuals and dialogue design

1 cs2341 lecture 5: task analysis robert stevens stevensr

Documents

task analysis basics

task hierarchy

task names

virtual decomposition

levels of task plans

ordering of tasks plans

tools clean rooms

new system slide