The output specification defines what the supplier is expected to provide but does not define the inputs or input costs. The output specification nevertheless defines the basis of the PSC in that the public sector must determine the inputs it would provide to meet the requirements of the output specification.
The output specification is derived from the business case that identifies the public sector's service requirements. The business case is essentially the reference project from which the PSC is constructed and defines the cost of the services if delivered by traditional procurement methods.