Task analysis analyses what a user is required to do in terms
of actions and/or cognitive processes to achieve a task. A
detailed task analysis can be conducted to understand the
current system and the information flows within it. These
information flows are important to the maintenance of the
existing system and must be incorporated or substituted in
any new system. Task analysis makes it possible to design
and allocate tasks appropriately within the new system. The
functions to be included within the system and the user interface
can then be accurately specified.
Provides knowledge of the tasks that the user wishes to perform.
Thus it is a reference against which the value of the system
functions and features can be tested.
The aim of ‘high level task decomposition’ is to decompose
the high level tasks and break them down into their constituent
subtasks and operations. This will show an overall structure
of the main user tasks. At a lower level it may be desirable
to show the task flows, decision processes and even screen
layouts (see task flow analysis, below)
The process of task decomposition is best represented as
a structure chart (similar to that used in Hierarchical Task
Analysis). This shows the sequencing of activities by ordering
them from left to right. In order to break down a task, the
question should be asked ‘how is this task done?’. If a sub-task
is identified at a lower level, it is possible to build up
the structure by asking ‘why is this done?’. The task decomposition
can be carried out using the following stages:
1. Identify the task to be analysed.
2. Break this down into between 4 and 8 subtasks. These
subtasks should be specified in terms of objectives and, between
them, should cover the whole area of interest.
3. Draw the subtasks as a layered diagram ensuring that
it is complete.
4. Decide upon the level of detail into which to decompose.
Making a conscious decision at this stage will ensure that
all the subtask decompositions are treated consistently. It
may be decided that the decomposition should continue until
flows are more easily represented as a task flow diagram.
5. Continue the decomposition process, ensuring that the
decompositions and numbering are consistent. It is usually
helpful to produce a written account as well as the decomposition
6. Present the analysis to someone else who has not been
involved in the decomposition but who knows the tasks well
enough to check for consistency.
Task flow diagrams
Task flow analysis will document the details of specific
tasks. It can include details of interactions between the
user and the current system, or other individuals, and any
problems related to them. Copies of screens from the current
system may also be taken to provide details of interactive
tasks. Task flows will not only show the specific details
of current work processes but may also highlight areas where
task processes are poorly understood, are carried out differently
by different staff, or are inconsistent with the higher level
Hackos, J. & Redish, J. (1998). User and Task Analysis
for Interface Design. Chichester: Wiley.
Kirwan, B. & Ainsworth, L.K. (Eds.) (1992). A Guide to
Task Analysis. London: Taylor and Francis.
Preece, J., Rogers, Y., Sharp, H., Benyon, D., Holland, S.
& Carey, T. (1994). Human-Computer Interaction. Reading
If the tasks are already well understood, it may be sufficient
to just identify and document the tasks as part of context
If other requirements activities
are complete, move on to design.
Shepherd, A. (1985). Hierarchical task analysis and training
decisions. Programmed Learning and Educational Technology,
Shepherd, A. (1989). Analysis and training in information
technology tasks. In D. Diaper, Ed. Task Analysis for Human-Computer
Interaction, pp.15-55. Chichester: Ellis Horwood.
Nielsen, J (1994) Extending Task Analysis to
Predict Things People May Want to Do