What is linking and what happens during the linking process? Attributional System Model
The "linking" is the process that produces a linked system model out of the unlinked multi-output Unit Process datasets of the ecoinvent database. The linking follows a series of steps; some of them are common for all system models, while others are specific to each system model. You can read more about the linking rules in the chapter 14 of the Data Quality Guidelines.
Common Rules
As simplified common rules: first, all the Materials for Treatment will be moved to the input side, with a negative sign. Then, all inputs and outputs will be linked to the corresponding market activities (unless an Activity Link has been specified as a Direct Link for the exchange). In the case of attributional system models, all suppliers will be linked to the markets, regardless their level of technology.
Specific Rules for Attributional System Models
Specifically in the allocation-based system models, all marketable by-products yielded in treatment activities will be moved into the activities producing the treated material for treatment as waste in a process called allocation at the point of substitution. Similarly, in the case of Specialty Productions, the reference product of the activity will be handled from now on as a by-product of an ordinary treatment activity.
Then, all multi-output activities are allocated (using the allocation criteria defined for the specific System Model). This allocation is happening at the point of substitution, and the marketable by-products issued in treatment activities get allocated in the activities they have been moved into.
After allocation, all activities producing the same marketable by-product yielded from a treatment activity get aggregated and are grouped into a single dataset that bears the original name of the treatment activity.
Video explaining APOS
This video explains, in a simplified way, how the ecoinvent version 3 database is linked in the "Allocation, ecoinvent default" system model and how allocation at the point of substitution (APOS) works. "Allocation, ecoinvent default" was renamed "Allocation at the point of substitution" in ecoinvent version 3.2.
What does the version number of the database mean?
What is an activity in ecoinvent version 3?
What are global background activities and where do they come from?
What is a market and how is it created?
In which situations are direct activity links used?
Why is the reference product of the treatment activities negative?
Why is the amount of the reference product changing?
What is linking and what happens during the linking process? Consequential System Model
What is allocation at the point of substitution (APOS)?
What do the shortcuts, such as CH, RER, RoW and GLO mean?
What does it mean, when the production volume of an activity is zero?
Why is the “Allocation, default” system model not available in the ecoquery anymore?
How do I calculate the amount of transport in the market?
What is the Rest-of-the-World (RoW) and how is it calculated?
Why is the LCIA score of a certain product negative?
What are the UUID numbers and how do they work?
How to interpret the uncertainty fields in ecoinvent?
What are the LCIA methods ecoinvent is publishing the impact assessment results for?
APOS: why do I have carrots on my recycled aluminium?