A homogeneous material with a definite composition.

Substance
identifier
Unique identifier
status
active | inactive | entered-in-error
category
What class/type of substance this is
code
What substance this is
description
Textual description of the substance, comments
instance
If this describes a specific package/container of the substance
identifier
Identifier of the package/container
expiry
When no longer valid to use
quantity
Amount of substance in the package
ingredient
Composition information about the substance
quantity
Optional amount (concentration)
substance[x]
A component of the substance