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Imagine a container half-full of parts on a factory floor. The container has a Kanban at-
tached to it. Goods are taken from the container, which is stored at the production
workstation, until it is empty. The Kanban in the empty container is then placed on a
Kanban board near the goods receiving area where it becomes a signal that the item
needs replenishment. The board has hooks in supplier order. When placed on the board
the Kanban becomes 'free'. The board has the Kanban system operation rules (Kanban
rules) clearly displayed. When a supplier's truck arrives with shipments of items to de-
liver, the driver checks the Kanban board and takes the Kanbans on the relevant hook
back to the supplier's site to authorise replenishment of these items next time around.
When the items are subsequently supplied, the Kanbans are returned to the work stations,
in the full containers, where they are used.
The deliberative theory of agency cannot relate at all to the Kanban system. The cards
do not consistently correspond to anything specific in reality. When they reside with
the parts they could be thought of as being a representation of these parts, although
they have no system purpose in this state and they will later actually refer to a different
group of parts. When they are free, they represent a stock shortage. When they are on
the Kanban board they are an authority to re-supply the parts. There are no records of
stock levels that we would expect to see in a deliberative approach.
Examining the system using the situational theory, a Kanban card represents part of the
activity of maintaining stock of a specific item. All of the Kanbans, together with the
rules by which they are used, provide simple ways of reasoning about stock. If many
of the same type of Kanban appear at the board then an undersupply may be occurring
or there may be trouble with the supplier's transport. An absence over a prolonged
period indicates a delayed manufacturing process. In addition to simple, reactive rules
for Kanban movement, the affordances of the physical nature of Kanban cards (they can
neither be created nor destroyed and they cannot be in more than one place at a time)
indirectly enforce all important replenishment business rules, in particular that there
can only be a fixed number of parts in the system.
The Kanban is rebound over time from one full container to a different full container
some time later. An interesting feature of this system that is the Kanban's meaning
changes according to where it is. When it is travelling back to the supplier it functions
as a request for an order from the manufacturer. When it is on the board it shows a
shortage of a specific item.
Common features of the systems
Each of the systems outlined above has features in common and that mirror the features
found described in situational systems literature: activities, situations, aspects of situ-
ations, environmental structure, and environmental affordances. We now examine each
of these characteristics, highlighting the approaches each system uses. We emphasise
interesting features that add practical depth to our understanding of the theoretical
constructs.
All systems use tokens to represent activities. Physical strips in landing aircraft represent
flights being landed. Rows on the whiteboard represent activities of making a compressor
at Cash. Cards in the Kanban system represent the activity of replenishing goods. None
of the tokens represent objects and properties in the way advocated in existing data
modelling methodologies. An interesting feature of these manual systems is the use of
positions of tokens to help actors in reasoning about activities. In the landing system,
the relative position of the strips helps the controller to reason about all landings. Kanban
cards on the board help operators to reason about goods shortages and priorities. The
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