Human-Computer Interaction
Task Analysis & Design
Alexiei Dingli
adingli@stmartins.edu
Task Analysis (1)
• Analysis the process in which humans play a role
• Study of systems in terms of human behaviour
• How people use such systems?
• What resources they use?
• What they need to know to use such systems?
• Involves
• Observation
• Recording
• Usage of that knowledge to build systems which
match user tasks & needs
Task Analysis (2)
• Not only confined to the computer element
• Tries to model all human activities involved
• Used in the initial stages of system design
• Clarification of required task
• Requirements capture
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•
•
•
Problems which we might encounter?
Which new features?
Which old features?
Innovation?
Task Analysis Techniques
• Involve sub-dividing/decomposing tasks into
• Meaningful
• Manageable units
• Such techniques include
• Hierarchical Task Analysis (HTA)
• Creates hierarchy & sequence of tasks, sub-tasks,
etc.
• Knowledge-based Task Analysis (KBTA)
• Creates ordered lists of components / tasks
• Systems analytic techniques
• Decomposes tasks but the ordering is focused more
on the system
Uses of Task Analysis
• Analytical method to determine how people
carry out work practices. It …
• Analyses how existing computer systems support
the tasks
• Identify & group user tasks in a structured fashion
• Design & implements prototypes
• Assist in the redesign of existing interfaces
• Help design support & training material
• Help in requirement analysis
HTA
(Annett & Duncan 1967)
• Most commonly used form of Task Analysis
• Graphical representation
• Decomposition of high level task into
constituent subtasks, operations, plans
• Uses structure chart notation
HTA Notation
Starting the Analysis
• Define the area of work
• Break it down into main tasks
• Break down main task into 4-8 subtasks;
specify subtasks in terms of objectives
• Draw subtasks as layered plans
Progressing the analysis (1)
• Choose level of detail
• Treat each branch consistently
• Decide at which level to stop
• “click mouse” v. “delete block of text”
• Choose depth-first, breadth-first, or combo
• Use hierarchical numbering convention
• 1, 2, 3, then 1.1, 1.2, 1.3 and so on ...
Progressing the analysis (2)
• Outline Plan for each task
• Describe how tasks are carried out (at the next
level)
• Number steps in the sequence they should be
followed.
Progressing the analysis (3)
• Types of plans include
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•
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Fixed Sequence
Optional tasks
Waiting for events
Cycles
Time sharing (simultaneously)
Discretionary (free will)
Mixtures
Finalising the analysis
• Check
• Consistency
• Accuracy
• Completeness
• Check numbering is consistent with
decomposition
• Check the accuracy of the notation
HTA Example 1
Hierarchy description ... How to clean the house?
• 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
HTA Example 1 Plans
• ... 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
HTA Example 2 Diagram
HTA Example 2 Refinement
HTA Example 3
• How would you go about preparing a Microsoft
word document?
HTA Example 3
HTA Example 3 Refined
HTA Outcome
• Manuals
• HTA provides structured information
• Helps users transfer between one system & another
• Requirements Capture
• Provide information on
• Existing operations,
• objects &
• ways of performing tasks
• Interface design
• Top level can be used as menus headers
• Task sequence can be used for user-system
dialogues
Exercise 1
• How would you go about sending an MMS
complete with text and image?
Knowledge-Based Task Analysis
• Creates taxonomies of a task
• Similar to generic hierarchies
• Aim is to classify
• Knowledge needed to complete a task
• Rather than
• Classify the procedures
• KBTA does not only show sequence but also
• Links between elements
• It provides a fuller model
KBTA Example 1
• Classifying motor vehicle controls objects
• Motor vehicle controls
• steering
• engine/speed
• direct
• gears
steering wheel, indicators
starter, accelerator, foot brake
clutch, gear lever
• lights
• external
• internal
headlights, hazards
roof light
• wash/wipe
• wipers
• washers
front, rear
front, rear
System Analysis Techniques (1)
• Data Flow Diagram (DFD)
• Describe flow of information between processes &
stores
• Adaptable to task analysis
System Analysis Techniques (2)
• DFD Example – Book Ordering System
System Analysis Techniques (3)
• Entity-Relational
Models
• Associated with
DB design & OO
analysis
• Similar to KBTA
since it describes
objects & actions
• But ERM explicitly
defines
relationships
System Analysis Techniques (4)
Requirements Gathering
• From several sources
• Existing documentation
• +cheap, -does not offer direct information
• Direct observation
• Informally watching, observing, monitoring, using specialised
recording equipment, walkthroughs
• Interviewing
• Elicit experts, to uncover task decomposition
• Questionnaire
• Answers to specific questions
• Quantitative survey data
• Qualitative survey data
• Group discussions
• Subjective data
Data Analysis – Card Sorting (1)
• Technique for exploring how people group
items, so that you can develop structures
that maximize the probability of users being
able to find items.
• Is easy and cheap to conduct
• Enables you to understand how 'real people' are
likely to group items
• Identifies items that are likely to be difficult to
categorize and find
• Identifies terminology that is likely to be
misunderstood.
Data Analysis – Card Sorting (2)
• Group the following elements together in 4 categories
and give each group a title:
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•
•
•
•
•
•
•
•
Films & Movies
Diving
Live Music
Hotel
Etiquette
Beaches
Architectural Sites
Night Clubs
Historical Monuments
Data Analysis – Kelly Grids (1)
• Ways of getting at the conceptual structure of the
problem space
• Identifying some 'elements' in the application
• These might be real things or concepts, but should be
organized into coherent sets
• For example, the set {Porsche, Jaguar, Rolls Royce, Mini,
Driver} has an obvious odd man out: Driver
• Elicitate new classes by
• asking for the opposites of all elements and concepts
• laddering to extract generalizations
• elicitation by triads extract specializations
• user is asked to take any three elements and specify a concept
that applies to two of them but not to the third
• For example, with {Porsche, Jaguar, Mini}, top speed might
emerge as an important concept
Data Analysis – Kelly Grids (2)
Other Data Analysis Techniques
• Noun-verb method
• Noun
• Verb
tasks-associated object
actions
John
Eats
Biscuit
• Rating Scales
• A scale based on descriptive words or phrases that
indicate performance levels
• Qualities of a performance are described (e.g.,
advanced, intermediate, novice) in order to
designate a level of achievement
Task Analysis + Interface Design
• Detailed TA can be mapped onto functions of a
system
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Menus
Selections
Sequences
Etc.
• Should be considered as an aid to design
• It is an iterative process
• User Oriented
• It does not try to understand the user but
• Observes behaviour + actions
Conclusion
• TA is an Iterative process which
• identifies new data
• Confirms existing data
• Rejects false data
• Necessary to understand tasks which in turn
is necessary for the design of the system
• It highlights the importance of the user
Exercise 2
• Produce a high-level hierarchal task analysis
showing how you would find information on a
website. Assume the site has a search facility
as well as normal links.
Exercise 3
• Consider the activity to make a telephone call.
Record the actions in an HTA diagram. Start off
simply assuming you know the number to dial.
Exercise 3
• Consider the activity to make a telephone call.
Record the actions in an HTA diagram. Start off
simply assuming you know the number to dial.
• What if you had to find the number in an
address book?
Exercise 3
• Consider the activity to make a telephone call.
Record the actions in an HTA diagram. Start off
simply assuming you know the number to dial.
• What if you had to find the number in an
address book?
• What if the number was engaged?
Useful Links (1)
• http://www.usabilitynet.org/tools/methods.htm
Useful Links (2)
• http://www.enquirewithin.co.nz/BUS_APP/busin
ess.htm
Suggested readings for next week
• Chapter 6 of Dix et al.