[Feature considered for implementation later: While the performance of the database service layer as described in this section has been implemented, additional experimentation and testing was found to be required before taking this feature into general use. It has therefore not been used in practice for any datasets in the version 3.0 release. Even without the software implementation, the specification in this chapter can be used for manual implementation.]
When one or more exchanges of an activity dataset are expressed as mathematical relations involving a property of the reference product, and this property is not a fixed property (see Chapter 5.6.7), the value of the property may change depending on the setting of the property in the dataset that has the reference product as an input. Each setting of the property value effectively represents a different product. This can be seen as a special case of combined production (see Chapter 5.3) in which each such property represents a combined product, with the important difference that the properties are not traded separately from the product that carries the properties. Like for other cases of combined pro- duction, a sub-division of the multi-product dataset is required, so that the specific dependencies of each variable property are expressed in separate datasets. For example:
If a dataset for impact extrusion of aluminium, with the reference product “impact extrusion of aluminium, cold”, has one or more of its exchanges defined as a mathematical relation to the property “number of deformation strokes” (variable name: “strokes”) of the reference product, two datasets are required: One with the reference product “strokes of impact extrusion of alumin- ium, cold” and one with the reference product “impact extrusion of aluminium, cold, property in- dependent”, in which the first dataset contains all the mathematical relations that involve the property “strokes” and the second contains all the other exchange data that are not dependent on this (or any other) property of the reference product.
If a dataset for waste incineration, with the negative reference product “waste”, has one or more of its exchanges defined as a mathematical relation to the property “cadmium content” of the waste, two datasets are required: One with the negative reference product “cadmium content of waste” and one with the negative reference product “waste, property independent”, in which the first dataset contains all the mathematical relations that involve the property “cadmium content” and the second contains all the other exchange data that are not dependent on this (or any other) property of the reference product.
For each new variable property of the reference product (i.e. a property included in a mathematical relation of another exchange), a new dataset is required (if there is at least one other activity dataset that has the reference product as an input with a different amount of the variable property). Each addi- tive element (summand) of the mathematical relation can only contain one property of the reference product. Composite or nested properties can be used for situations where multiple relations exist (e.g. when an emission is dependent on both the degradability and the elemental composition of a waste). Figure 11.10 illustrates the original and the derived datasets and how these are linked to the activities that require the reference products. The variable property is added as a by-product with the name “[property name] of [name of reference product]” and the mathematical relation is changed to refer to the amount of this new by-product, while the original property is deleted from the reference product, which is renamed to “[name of reference product], property-independent”. All exchanges that were originally expressed as fixed amounts are re-formulated as mathematical expressions relating to the reference product, i.e. the fixed amount “40” translates to “40/A”, where A refers to the amount field of the reference product. The market activity dataset for the reference products is likewise sub- divided, with all other exchanges and properties remaining with the property-independent reference product, so that the new property-specific market activities have no additional exchanges besides the reference product.
Figure 11.10. The original and derived datasets where a property Y of the reference product is used as a variable, and the original dataset requiring this reference product, but with a different value for Y, where the input is also subdivided. Note that the mass balance (and other balances) may be kept intact for the subdivided activi- ties, (as illustrated by the change in dry mass of the reference product) when such adjustments are made during a manual sub-division, but since properties do not themselves have properties such as mass, such adjustments are not made when the sub-division is made automatically by the database service layer (see Chapter 14.1, linking rule no. 4). However, the aggregated systems results are not affected by this.
Other datasets supplying the same reference product to the same market are subdivided in the same way. If such datasets do not have the same property of the reference product as a variable property, the exchanges of this dataset are interpreted as independent of this property, and their fixed amounts thus simply re-formulated as mathematical expressions relating to the re-named reference product. When the subdivision is performed by the database service layer, the subdivided datasets keep the same activity ID as the original dataset, which implies that the product name is required to distinguish the datasets from each other.
product A product A 2 kg product A;
property Y = 3g/kg
1 kg reference product A; dry mass = 1 kg; property Y = 5g/kg Original datasets:
Activity
producing A Exchange B; amount = f(A, property Y) = 0.25 + 0.8*Y g Exchange C; amount fixed (40g per kg A)
Activity requiring product A
Derived datasets and links to supply 2 kg of A: 6 g property Y of reference product A Activity producing property Y of A Activity producing A, property independent
Exchange C; amount = f(A) = 2 kg *40 g/kg = 80 g Exchange B; amount = f(Y) =
0.8*Y g = 0.8*2kg*3g/kg = 4.8 g Activity
requiring product A 2 kg reference product A,
property independent; dry mass = 1.994 kg
Exchange B; amount = f(A) = 2*0.25 g = 0.5 g Market for product A Market for product A Market for property Y of product A (new)