Greg Low describes a common business problem:
But while food wholesale systems will need to deal with quantities like I described in that post, they often have another layer of complexity. Items are often sold by:
- Quantity
- Weight
- Quantity and Weight
This is an interesting look at how the domain can drive what a proper solution looks like. It also seems like a good use case for 6th normal form, with unit quantity and unit weight tables to prevent NULL from cropping up.