Budget Line follow the variation API, this means that we have to define:
What are the variation base categories
What is the variation range for each category
What are the selected variations for each category
To achieve this, we use some Budget Model documents which contains Budget Variations. Budget Variation is used to configure the variation base category, and the variation range. There are two types of budget variation: Category Budget Variation which takes the base category and the variation range from possible values of a category, and Node Budget Variation, for which the base category must be configured, and where the variation range is defined either by a script, or by selecting possible nodes in the budget variation itself.
When a budget is created, it is associated to a budget model, and when budget lines are added to this budget, the budget model is used to initialize the budget lines and set the variation base categories. The view of a budget line uses a parallel list field to display the variation range for each category, and allow the user to select the variations. Again, budget variations will be used to list the variation range.
A matrix box will show cells for the selected cell range, to enter quantities or price for each budget cells. Budget Variations are used to return the cell range.
Budget Variations can also be used at the level of a budget, to define a main category of a budget (and for example define security based on this category, or limit the scope of budget lines to the category defined on a budget). Budget Variations can also be used at the level of a budget line, to set a category on the line itself (a matrix can only show 3 dimensions).
Currently, a budget has a resource defined on it, and the budget cells shows quantity expressed in the default quantity unit of this resource. This means that:
We cannot use resource as a budget variation axis
We cannot use resource_category as a budget variation axis
We cannot make a budget on prices