The bill of quantities database is organised into "Items" grouped into chapters. These units are measurable and contractable components and can be valued based on experience, breakdown into basic concepts, or using price tables published by third parties.

When a unit is quantified in the bill of quantities, it is called an "Item".

Chapters allow the bill of quantities to be organised, structuring the "Items" according to the planned order of execution of the job, and cannot be repeated in the "Breakdown tree".

Bill of quantities hierarchy tree

The scheme of successive breakdowns of budget concepts can be likened to an inverted tree structure, where the trunk would be the root concept (associated with the name of the budget file), while the branches would be less complex concepts, such as "Work sections", "Sub-work sections", "Items", "Units" and "Auxiliaries".