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all of the information required to land the flights that are under control. It is the struc-
turing of the controller's environment using the strips that shows information beyond
that which is on the strips themselves. For example, the way the strips are stacked in
Figure 14.3 means something specific for the controllers and helps them to remember
and reason about the flights they are landing. Handing over control of flights from one
controller to another is achieved by passing strips and is facilitated by how the room is
laid out, and such handovers seldom include verbal exchanges. The limited space where
strips can be placed alerts the controller to busy situations because room for new strips
is then hard to find. In these situations controllers will hold new strips in their hands.
Controllers sometimes write their own strips when unusual things occur, relying on the
convenience and flexibility of paper.
Analysing this system using the deliberative approach is not straightforward. No repres-
entation is tied to a specific object. Each strip is about landing a flight rather than the
flight itself or the aeroplane. Together, the strips are about the activities of landing that
are under the control of the controller. None of them describes a flight enough to say
that they represent an object in the sense of the deliberative approach to modelling.
In contrast, this system is easily related to the situational theory of agency. The strips
represent the activity of landing a plane and, together with other strips and their relative
position, these are sufficient to enable a controller to appreciate the current situation
and to select actions. This, in our view, is a more plausible explanation than one based
on the deliberative theory of agency.
Small-scale efficient 'cottage' manufacturing: the Cash Compressor System
A small factory (Cash Engineering Research) manufactures air compressors and has built
up a system for doing so over several years. The workers in the factory have played an
active role in designing the system. Known as the Cash Compressor System, the system
is for production control in a small factory of four staff manufacturing about 200 air
compressors a year. The system has a whiteboard that represents non-routine aspects
of the compressors being made. There are no computers in the factory. What is interesting
is how little information is represented on the whiteboard without compromising control
or efficiency.
The factory is designed so that the person taking orders on the telephone in the middle
of the factory has full view of all available stock hanging on shelves lining the walls.
The main components of the system include a whiteboard of open customer orders and
the physical parts of the air compressors that, by their construction, implicitly contain
information about their own method of manufacture. The information on the whiteboard
is job-specific including name of client, and options such as colour, and compressor
motor size. The system has been designed deliberately in this way to reduce the need
to represent things.
Manufacturing commences when the order is received by phone and a line order is added
to the whiteboard. The parts for making the customer's compressor are checked for
availability visually, and if need be, ordered on a one-off basis. The machine assembler
then takes a machine base and begins construction, referring to the whiteboard only for
order-specific information that is not part of the standard assembly routine.
What is interesting in the Cash System is what is not represented. There is no information
about how to construct the machine: the machine acts as its own 'jig' through devices
for guiding a tool or part to a specific place. Employees have learned the limited number
of techniques used with the 'jig'. There is no parts-list or inventory system: the availab-
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