Build accounting models

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Building models

Models can be edited by Admin users in the Model Editor using a YAML-based scripting language.

• Open the Model Editor by clicking on Edit/Test besides the model name

The YAML script constructs carbon accounting models using a tree of interconnected nodes, where each node performs a calculation or holds a value. These nodes are organized in a hierarchical structure.

nexus_nodes_attributes:
- name: Output Node
  operator: summation
  data_point_type: output-slug
  nexus_nodes_attributes:
  - name: Intermediate Calc A
    operator: summation
    nexus_nodes_attributes:
    - name: Data Input 1
      data_point_type: data-point-slug
    - name: Constant
      constant: 100
  - name: Intermediate Calc B
    operator: difference
    nexus_nodes_attributes:
    - name: Static Input
      order: 0
      data_point_type: static-input-slug
    - name: Data Input 2
      order: 1
      data_point_type: data-point-2-slug

This is the equivalent of writing the following equation:

$(Datapoint1 + 100) + (\alpha - Datapoint2) = Output$

As a best practice, Validate the model you have built, and check the results in the Console before saving the model.

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Editing models

Saving the model updates its version.

New model versions do not affect the calculations of past accounting batches, only new calculations run after the version has been created.

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Defining new nodes

Nodes can be added to the model to represent specific variables in the accounting equations. Each node can:

• Receive a value from a data source (data_point_type)
• Use a constant/mapped value from a library, or
• Have its value calculated from child nodes through the defined operator

    - name: Input Node
      data_point_type: {{input-data-point-slug}}
    - name: Static Input Node
      data_point_type: {{static-input-slug}}
    - name: Constant Node
      constant: {{value}}

See Reference below for the full list of parameters that can be defined on each node.

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Units

Units are not always required to be defined on nodes, but are very helpful for legibility especially when data is run through operator expressions. Use output_unit to define the expected result unit:

nexus_nodes_attributes:
- name: Calculated EF
  output_unit: tCO2e/tonne
  operator: quotient
  nexus_nodes_attributes:
  - name: Emissions
    order: 0
    output_unit: kgCO2e  // note that Mangrove supports unit conversion above
    data_point_type: emissions-datapoint-slug
  - name: Mass
    order: 1
    output_unit: U.S. ton  // note that Mangrove supports unit conversion above
    data_point_type: mass-datapoint-slug

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Testing models

Models can be tested by running them with a set of inputs to confirm the calculations.

How to test the models:

• Open the Model Editor by clicking on Edit/Test besides the model name
• Switch to Test Model
• Define a time range (this is necessary for certain calculations that consider duration), enter values for the model’s required inputs, and Run Test
• Review the output calculations in the Console

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Reference

Below is the full list of fields that can be configured on nodes within a model.