Bill Of Material
A bill the material defines what parts or components are used to manufacture a product. In opentaps, you can define a bill of material of unlimited depth, meaning that the components could themselves be manufactured from lower-level components without limitation.
Each bill of material component has a quantity associated with it which defines how many of this component is used for one of the manufactured product. For example, a laptop could have one screen and two USB ports associate with it. In this case, the quantities would be one screen to one laptop and two USB ports to one laptop.
Bill of material component quantities can be fractions, which may cause fractional quantities to be required when the finished product is being manufactured or planned.
You can also define fractional quantities in a bill of material to model relationships, where a large batch of something is used to make smaller batches. For example, 1 pound of bulk milk powder could be used to manufacture 1/16 of a retail bag of powder. This, however, may cause small rounding errors, depending on the quantities involved.
Finally, a bill of material component could also have a scrap factor associated with it. The scrap factor is used in Materials Resource Planning to prepare additional quantities for production. For example, if a bill of material component has a quantity of 2 but a scrap factor of 50%, Materials Resource Planning and build material simulations will say that 3 of this component is required per 1 finished product. The scrap factor could also be a negative number to be used as a "salvage factor," in case the part could be salvaged from some existing stockpile instead of ordered or manufactured again. For example, a bill of material component has a quantity of 2 but a scrap factor of -50%, then only 1 will be required per each finished product.