The special activity types are: 0 = “ordinary” transforming activities. Transforming activities are human activities that transform inputs, so that the output of the activity is different from the inputs, e.g. a hard coal mine that transforms hard coal in ground to the marketable product hard coal. Transforming activities are here understood in the widest possible sense, including extraction, production, transport, consumption and waste treatment activities, i.e. any human activity where the intermediate output is different from the intermediate input. The concept “transforming activities” is introduced here simply to distinguish – in the further modelling and linking of activities – these “ordinary” activities from the market activities, production and supply mixes, import and export activities, and correction datasets.1 = market activity. Market activities do not transform their inputs, but simply transfer the intermediate output from a transforming activity to the transforming activities that consume this intermediate output as an input, e.g. from hard coal at the supplier to hard coal at the consumer. Market activities typically mix similar intermediate outputs from different transforming activities. Market activities therefore supply consumption mixes of the intermediate outputs.10 = market group. Market groups are to markets what markets are to transforming activities. In the undefined system model a market group only contains a reference product. The linking algorithm will add supplying markets as inputs which are contained in the location of the market group and have the same reference product.2 = IO activity. An IO activity represents an activity dataset from a national supply-use table, i.e. typically the supply and use of one specific industry.3 = Residual activity. A residual activity is the resulting activity when subtracting all available unit processes within an activity class from the supply-use data (IO activity) of the same activity class, for the same year and geo-graphical area. 4 = production mix. A production mix represents the production-volume-weighted average of the suppliers of a specific product within a geographical area.5 = import activity. An import activity represents the import of a specified product to a specified geographical area, solely for use in national balancing (not contributing to any auto-generated consumption mixes). Imports to administratively constrained markets and from partly isolated markets are modelled as ordinary transforming activities in order to be included in the relevant market activities (consumption mixes).6 = supply mix. A supply mix is a production mix with the addition of the import of a specified product to a specified geographical area.7 = export activity. An export activity represents the export volume of a national production mix that has the national area as its geographical location and does not contribute to any auto-generated consumption mixes. To give the correct value of the export, the same activities and data that are included with the market activities are added directly to the export activity. This includes transport activities, production losses, wholesaler and retailer activities, and product taxes and subsidies.8 = re-export activity. A re-export activity represents the re-export volume of a geographical area and does not contribute to any auto-generated consumption mixes.9 = correction activity. A correction activity is an activity that is added twice to a product system, one with a positive and once with a negative flow, in order to move one or more exchanges from one part of the system to another, e.g. to correct for downstream effects of an upstream activity, or to correct a bias in the mass-balance introduced by an allocation. More details on this is provided in the Chapters on "Downstream changes caused by differences in product quality" and "Allocation corrections" in the ecoinvent Data Quality Guidelines.