1. Preece Chapter 7.7 & Mc Cracken Chapter 3
Task Analysis
Preece Chapter 7.7 & Mc Cracken Chapter 3
JTBurns 2004

2. User interfaces are designed for..
a new system to replace an existing manual system e.g. library information system
an existing computer system being redesigned
functionality remains the same
functionality is extended or changed in some way.
a completely new system with no manual equivalent (generally rare)
There is usually some situation with existing users and usage that can be studied and analysed.
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3. Task Analysis provides an essential basis for
early stages of interface design
evaluation of design at early and late stages
structuring training in system use
structuring and design of documentation
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4. Levels of Task Analysis
relate to existing situation or new system.
General Analysis of User Characteristics
Detailed Analysis of tasks in present job(s)
Subset of tasks to be included in new system
Analysis of Actions and Objects in new system
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5. General Analysis level
who are the users
classify the users into one or more groups
define characteristics of the group
what are the main task components of the users’ present job
what proportion of time is spent in different tasks
what causes variations in this
where are the tasks carried out
what equipment (other than the computer system) are used
what communication is there between the user and other people
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6. Detailed analysis of tasks in present job
what is the hierarchical structure of main tasks, and subtasks within these main tasks
how do users see the structure of their job in terms of tasks
for each task identified
what information is required
what actions arise or result from decisions
what feedback is provided on effect of actions
what affects successful performance
what are the possible errors and what factors cause these
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7. Requirements for a task analysis method
a structure to represent goals, subtasks, procedures, objects and actions
a means of collecting data from experts in the task domain
a means of representing the analysis to
check validity of the analysis back with experts
communicate with others in design team
guidance for mapping the analysis to the design
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8. Detailed analysis of tasks in present job
what are the good features of the existing system which should be retained in the subsequent redesign
what are the bad features of the existing system that should be designed out
what skills are required for each task
how are the required skills trained initially and how are these retained
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9. Objectives of task analysis to support interface design
identify a hierarchy of user goals, tasks and subtasks together with a plan describing how and when these are done
represent lowest level task as a set of procedures include statements of information requirements and exception conditions
identify set of actions and associated objects
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10. Hierarchical Task Analysis
Involves breaking a task down into subtasks, then sub-sub-tasks and so on. These are grouped as plans which specify how the tasks might be performed in practice
HTA focuses on physical and observable actions, and includes looking at actions not related to software or an interaction device
Start with a user goal which is examined and the main tasks for achieving it are identified
Tasks are sub-divided into sub-tasks
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11. Example Hierarchical Task Analysis
0. In order to borrow a book from the library
1. go to the library
2. find the required book
2.1 access library catalog
2.2 access the search screen
2.3 enter search criteria
2.4 identify required book
2.5 note location
3. go to correct shelf and retrieve book
4. take book to checkout counter
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12. Example Hierarchical Task Analysis (plans)
plan 0: do If book isn’t on the shelf expected, do
plan 2: do If book not identified do
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13. Example Hierarchical Task Analysis (graphical)
Borrow a book from the library
plan 0: do
If book isn’t on the shelf expected, do
go to the library
find required book
retrieve book from shelf
take book to counter 1 2 3 4
plan 2: do
If book not identified from information available, do
access search screen
enter search criteria
identify required book
access catalog
note location
2.1
2.2
2.3
2.4
2.5
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14. Hierarchical task analysis (HTA)
Structural components
goal - statement of a desired state to be achieved
e.g. obtain a printed balance from an ATM
operation - things done in order to achieve goals
e.g. produce a paper copy
sub-operations- subordinate operations to attain main operation
plan - specifies when the conditions when each sub-operation will be carried out
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15. Hierarchical Task Analysis
Aim is to describe a task in terms of a hierarchy of operations and plans where
operations = Goal-Task-Action
plans = specification of conditions under which (sub) tasks are carried out
Advantages of HTA
simple, informal notation
but still requires considerable skills on part of analyst.
Can be captured graphically
using a form of structure chart
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16. Partial HTA chart for Editing Text in Windows
0. Edit Text
Plan 1: According to Requirements
1. Cut Text
1. Use Menu
option
2. Use Hot-key
Combo.
3. Use Toolbar
Icon
4. Use Delete
Plan 1.2: 1,2
1. Select Text
2. Press Ctrl + X
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17. Means of collecting task analysis data
interviews with potential users
observations of users performing tasks by trained observers
activity sampling
activity logging (by observer)
activity logging (by user) - 'diary of activities'
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