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these systems that add to our understanding of the practical application of the situational
theory. We discuss each of these below.
Each of the systems confirms activities, situations, actions, environmental structure and
environmental affordances as important ontological categories for situational systems.
Fundamentally, activities, not objects, are represented in these systems. Situations and
aspects of situations are shown to actors so they can select actions or reason about their
activities. Environments are structured and use affordances that increase the reliability
of the goal of an activity being realised. The relationship between environmental structure
and affordance is sometimes complex. This is seen in the Cash System where the machine
is its own jig. The jig is designed so that the environment of the worker changes in such
a way that precisely one situation is returned.
A characteristic emerging from the study is the extensive use of physical tokens (e.g.
strips) to contain information about situations and activities and to facilitate reasoning.
Tokens often represent different situations according to their physical relationship to
other tokens, and their physicality aids reasoning about situations for human actors.
The need for manipulation in situated reasoning is an important feature of these systems
and cannot be ignored when designing a methodology for situational systems.
Physical tokens are also used to hand over situations to other actors involved in an
activity. This is illustrated in the flight landing system where controllers routinely hand
strips to other controllers. Successful handover is helped by the receiving controller
having to physically handle the token.
In these systems tokens and other parts of an agent's environment play a critical role in
representation. A human agent uses tokens in the environment to reason about activity
and to notice situations. Tokens contain some, but not all, information about situations
and activities. Often it is the relationship between tokens that completes the picture for
an agent. Contrastingly, deliberative systems require a model of the world where objects
and their properties are self-contained and correspond with objects in the human agent's
environment.
The use of physical tokens requires that careful attention is given to the capabilities of
computerised technology such as mobile devices when designing information systems.
Poor selection of devices that do not deliver the required palpability, capacity for ma-
nipulation, or representational ability may place the success of the whole information
system in danger. Further, environments of computerised parts of the information system
must be carefully designed with these findings in mind.
Following our examination of manual situational systems, the methodology still consists
of six steps. The details of specific steps, however, must be augmented with results from
our analysis of the systems. These largely give insights into the implementation of Stage
6 in the method. First, in the manual systems explored, physical tokens are often em-
ployed by agents to represent parts of activities and contain information about situations.
These are seen to be important for both situation recognition and for reasoning about
action. Arguably, they do not reduce simply to the information displayed on them
(Mackay et al., 1998). This gives an important insight into the unique character that the
informational component of situational systems should possess. Although not all situ-
ational systems may need to employ the idea of physically manipulable tokens as the
representational component of the system, it seems that it is a prudent approach to
consider this possibility in conjunction with information and communication technology
as a possible form that part of the information system might take. For instance, in a follow-
up study of the manual air traffic control system described above, Mackay et. al. (1998)
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