Human-Computer Interaction and Presence in Virtual Reality

Chapter 3
object could be a text document and task behaviors could be typing, reading documents,
moving text etc.
A task is a set of behaviors directed towards a task goal. A task goal can be either a work
goal or an enabling goal. A work goal is related to a change in the work domain, an enabling
goal relates to a change in the structures designed to support the tasks, for instance loading
the text-processing software. A TM describes part of the TA domain. Unfortunately, the
different methods use different terminology, making comparison complicated.
Usually a TM will contain a description of the task behaviors. Methods such as Hierarchical
Task Analysis (HTA) (Annet & Duncan, 1967; Shepher, 1998), Groupware Task Analysis
(GTA) (van der Veer & van Welie, 1999), Méthode Analytique de Description (MAD)
Figure 3.3: Partial task decomposition using the GTA method. ‘And’ denotes
the subtask can be performed in parallel, ‘seq’ indicates the tasks must be
performed in sequence.
(Sebillotte, 1995), GOMS and User Interface Modeling (UIM) (Lif, 1999) uses a hierarchical
decomposition of the tasks, where top-level tasks are divided into subtasks. The lowest level
tasks are often called “unit tasks” 4 . These tasks can be further divided into actions. These
differ from tasks in that actions derive their meaning from the task they are a part of; they
have no meaning on their own. Users are seldom aware of the actions that are part of a
specific task. The hierarchy usually also includes information on the sequence in which the
tasks are executed, see for instance figure 3.3. Other methods, such as Contextual Design
(Beyer & Holtzblatt, 1998) do not use an explicit decomposition but focus more on
sequence, using an explicit sequence model.
In the previous description the term “task” was used, even though some of the methods
mentioned use the concept “goal”. This is no big difference, since tasks and goals in most
frameworks have a one-on-one relationship (van der Veer & van Welie, 1999).
Several methods, such as Contextual Design, GTA and UIM also include a description of the
objects of the work domain. Task can then be related to these objects. Furthermore, the three
methods mentioned here also allow tasks to be related to roles 5 that can be performed by
4 GTA distinguishes between "unit task", which is the lowest task level that people want to
consider in referring to their work, and "basic task", which is the unit level of task
delegation, is defined by the tool that is used in performing the work, like a single command
in a command driven application.
5 GTA and Contextual Design refer to sets of tasks that can be assigned to an actor as 'roles'.
UIM uses the term 'work situation' for a very similar concept.
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