Why is the target document model included in the precomputation model?

Kernel
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1

I’m having a look at the document mapping feature of kernel in 2025.06. I have setup a workspace to test the modeling part. In the workspace I have created document models Foo and Bar that each contain just a root group with a single string field.
Then I have setup a mapping model whose purpose is to map from Foo documents to Bar documents like this:
image
The intention is to combine 2 Foo documents to a single Bar document.
When adding a precomputation model I also get to see an include of the Bar model:
image

I would like to know why the Bar model is included in the precomputation model and what purpose it does have?

I am wondering because I first just added a computation of the /General/Value field in the precomputation model. But then the Mapping Model editor just said that the model is invalid without any further notification of what the actual problem is. The precomputaiton model was also shown as valid when it was opened.
From reading the documentation I could after some time inferr that there are helper fields supposed to be used in the precomputation model. But then why would it be useful to include the target document model?

2

@andreas-fresh-mesa: The target DM is included in the precomputation model since you might want to have computation alternatives depending on the state of the target document, e.g. let’s assume you have the field General/FieldA in target DM, with that in mind, you could write following computation:

  1. precondition: FieldFilled(/General/FieldA)
    operation: [/FirstFoo/General/F1] + [/SecondFoo/General/F1]
  2. precondition:
    operation: [/SecondFoo/General/F1] + [/FirstFoo/General/F1]
3

The target document that is present at the beginning of the mapping can contain data already.
If you want to react on this data, you can use a respective precomputation (as @gildardo-cached-canyon wrote)