Inquiry about Compliance Unit interfaces

It seems that the compliance-unit is a fixed size data structure with references for data (I.E. pertinent data is not stored in the structure itself).

Given this information I’m not sure how the interface is supposed to work:

For example

sig created  : compliance-unit -> set commitments
sig consumed : compliance-unit -> set nullifiers
s :

these functions can not exist without the action it is apart of being passed in no?

I might just be misunderstanding this.