Date post: | 28-Dec-2015 |
Category: |
Documents |
Upload: | thomasine-cameron |
View: | 215 times |
Download: | 0 times |
Gary Marsden Slide 1University of Cape Town
Human-Computer Interaction - 5
Requirements
Gary Marsden([email protected])
July 2002
Gary Marsden Slide 2University of Cape Town
Unit Objectives
We shall cover– Different forms of task analysis
• Procedure Based• Object based• Relationship based
Rationale:– In any lifecycle, it is important to get the
problem defined well at the start• Mistakes at this stage can be costly to rectify
Gary Marsden Slide 3University of Cape Town
Requirements Analysis
There are two things we need to say at the outset
Users don’t always know what they wantProgrammers don’t always know what is
best for users– Need methodology to understand the problem
Gary Marsden Slide 6University of Cape Town
Where to start
All lifecycles start by trying to quantify what the problem is
In HCI, we have a number of tools to do this– Analysis of the wider system (Task analysis)– Analysis of the user (human models)– Design guides and standards
Gary Marsden Slide 7University of Cape Town
Task Analysis
Common to most software engineering efforts
Focuses on the perspective of the user– what people do– what things they work with– what they must know
Gary Marsden Slide 8University of Cape Town
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.
Gary Marsden Slide 9University of Cape Town
Task decomposition– splitting task into (ordered) subtasks
Knowledge based techniques– what the user knows about the task
and how it is organised
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
Different Approaches
Gary Marsden Slide 10University of Cape Town
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
Gary Marsden Slide 11University of Cape Town
Example Decomposition
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
... 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
Gary Marsden Slide 12University of Cape Town
Generating hierarchy
get at 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 small Motor actions: lowest sensible level
Gary Marsden Slide 14University of Cape Town
Knowledge-based Analysis
HTA is focused on procedures; KBA is based on objects and actions
Build taxonomy out of objects Relationships are either:
– XOR: exclusive– OR: In more than one branch– AND: Must have all branches
Gary Marsden Slide 15University of Cape Town
KBA example
Wash/wipe AND– Function XOR
• Wipe – Front wipers, rear wipers• Wash – Front washers, rear washers
– Position XOR• Front – front washers, front wipers• Rear – rear washers, rear wipers
Kitchen item OR– Preparation – mixing bowl, plate– Cooking – frying pan, saucepan– Dining – plate, glass
Gary Marsden Slide 16University of Cape Town
KBA applied
So what?• Well, there is a close correlation between hierarchy
and interface objects• Where would you put “Insert Table”
Gary Marsden Slide 17University of Cape Town
Entity-Relationship
Very common technique, especially for databases
Won’t dwell on it here, but note that when used for HCI, includes non-computer objects
Good at identifying interface objects and functional relationships between objects
Gary Marsden Slide 18University of Cape Town
Outputs from task analysis
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
Gary Marsden Slide 19University of Cape Town
More Output
Requirements capture and systems design– lifts focus from system to use– suggests candidates for automation– uncovers user's conceptual model
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
Gary Marsden Slide 20University of Cape Town
Summary
We have looked at trying to understand the tasks of a particular problem– By considering the procedure of the task– By considering the objects used in the task– By considering the relationships between
objects
We have also briefly looked at what purpose each type of analysis might be put to.