Gary Marsden Slide 1University of Cape Town

Human-Computer Interaction - 5

Requirements

Gary Marsden(gaz@cs.uct.ac.za)

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

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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

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Programmers are people?

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What programmers see

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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

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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

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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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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

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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

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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

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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

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Diagrammatic Form

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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

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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

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KBA applied

So what?• Well, there is a close correlation between hierarchy

and interface objects• Where would you put “Insert Table”

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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

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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

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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

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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.