7 . Task analysis

(Preece: Chapter 20)

This chapter deals with task analysis - how tasks that the user is supposed to perform using the system can be described - what concepts are used in the modelling.

The concept of task has many meanings - from the overall job definition to single operations on keyboard. Here we use a three level concept structure

Goals
Tasks
Actions

A Goal can be defined as something the user wished to achieve. Goal can be for example: write a letter - make an order - deposit money. To reach a goal the user usually needs a plan which involves a set of tasks to be performed in order to reach the goal.

A Task is the series of activities or actions required to achieve a goal. A task is a structured set of activities. The task can involve problem solving or selecting between alternative actions (or sub tasks)

An Action is a 'simple task' which requires no problem solving. An action has no structure

The tasks can be described as hierarchies. For example the use of a word processing system can be described as a hierarchy of subtasks which can be taken alternatively or after each others in order to reach the overall goal.

Task analysis steps
Goal -> What to do
Select the Device or Method -> Determines the task in concrete terms
Task -> activities to achieve the goals using the device
Subtask - components of a task
Actions - simple tasks

Hierarchical task analysis

Hierarchical task analsysis (HTA) is a simple method for describing the hierarchical tasks and subtasks. For a task we can describe into which subtasks it can be partitioned. A plan can be assigned to each task. See figure 20.2.(handout)

A HTA can be described in three steps: Starting - progressing - finalizing

Starting the analysis

Specify the main task
Break down into 4 - 8 subtasks. Tha subtasks should be desribed as objectives - Should cover the whole main task
Draw subtasks as a layer. Make a plan how subtasks are connected.

Progressing the analysis

Decide on the level of detail (detailed: keystroke-level - higher: general tasks)
Decide for each task if the analysis should be continued
Number boxes according levels

Finalize the analysis

Check decompositions - all alternatives covered
Show the decomposition to an expert (evaluation - assessment)

Modelling 'how-to-do-it' knowledge

How to model procedural knowledge - how a user selects the appropriate steps to perform a task.

A well known method is GOMS (Goals, Operations, Methods, Selection rules) (by Card and Moran, 1983).

If the user knows what should be done - what the goal is, he should be able to use his knowledge on the task domain to decide what to do - what methods to use what actions to take.

See figure 20.3 (handout) to see how File manipulation can be described in the DOS environment and Macintosh - environment

What are ther main differences of these tasks.

Analyse the differences in terms of what the user has to know to be able to do these tasks.

Purpose of task analysis

Describe the logic how the users can use the system. Analyse differences of interfaces. We can analyse the logic of the interaction - if the tasks can be done using same kind or reasoning and using same kind of knowledge.

Formal Language Grammar in task analysis

The tasks can be desrcibed as a hierarchy of nodes. This takes up space and is not practical when describing large and complex tasks. The Formal Language Grammar is a suitable method for large tasks.

The method

Action = elementary task, can not be partitioned in subtasks

Described as text (UPPER CASE) or a symbol (mouse click, move cursor, point,...)

Task = sequence of actions or tasks (subtasks)

Described as a rule.
Task has a name <taskA> , <taskB> written in brackets.
The rule is desrcibed as follows

<taskA> := rule

The rule consists of elements that can form a sequence

<taskA> := <firsttask> + <secondtask> + <thisrdtask> .....

the elements of the rule can be alternatives

<taskA> := <firstchoice> | <otherchoice> | <thirdchoice>

this means that the task taskA can be performed by doing firstchoice or otherchoice or thirdchoice.

the operators + and | can be combined in the same rule.

<A> := (<B> + <C>) | <D>

Alternatives can be written as alternatives in one rule or as separate rules. The example above can be written also as two rules

<A> := <B> + <C>
<A> := <D>

This means that if we want to do A we can use either of the rules, we can do either B and C or we can do D.

A more extensive example.

How to make a word of a text to boldface.

<bold-a-word> := <select-a-word> + <do-bold>
<select-a-word> := POINT-WORD + DBLCLICK
<select-a-word> := POINT-START-OF-WORD + MOUSEBUTTONDOWN + MOVE-TO-END-OF-WORD + MOUSEBUTTONUP
<do-bold> := LOCATE-BOLD-ICON + CLICK
<do-bold> := <find-bold-in-menu> | CTRL+B
<find-bold-in-menu> = LOCATE-FORMAT-MENU + MOUSEBUTTONDOWN + LOCATE-STYLE + LOCATE-BOLD + MOUSEBUTTONUP