When we first considered the classification of resource input bases for transformations, we were only really considering conventional persistent resources. The thinking clearly changes if a resource is consumable, as the interpretation of the
Used Capacity
result in particular must be aggregate by definition. While it is tempting to think that all the other bases should be classified as aggregate too, it is not quite so clear cut when you consider that results such as
Installed Capacity, Slack Capacity and even
Used Up Capacity
must be consolidated to a last period result if a consumable resource has a shelf life and the unused capacity (and already used-up capacity) persists beyond the current period.
Only if the lifetime were zero could these other results be considered as ‘aggregate’. In order to avoid this potential ambiguity, our assumption is that the only well-defined and useful bases for a consumable resource input to a transformation are
Used Capacity, Incremental Capacity,
Incremental Units and
Capital Expenditure
(all of which will be classified as aggregate). Any other choice of input basis will be treated as an error for the time being.
For a consumable resource, the Capital Expenditure
basis will indicate Stock Purchased.
There is an additional special case of a resource transformation as an input to a service to define a value chain. Historically, this was only allowed for the (instantaneous)
Customer Base
input, which was fine when all resources were implicitly persistent. However, it will not be appropriate to drive this input by a consumable resource if the associated transformation is assumed to be aggregate. Not only will STEM 7.3 treat such a connection as an error, but it has to allow the
Traffic per Connection
input to establish such a value-chain connection instead (note: this is still work in progress).
Similar logic means that any other input which can be driven by a transformation, such as the
Sites
input for a location or the Planned Units
input for a resource, will also need to be checked to ensure that the transformation has a suitable output mode.