A "Bill of Materials" $($BOM$)$ defines the standard quantity of each sub$-$component type

that is used to manufacture a component type. Information about a component type can

be recorded before it is used to manufacture any other component type. The same sub$-$

component type can be used for manufacturing more than one component type and can

thus occur in more than one BOM specification. A BOM is defined for each component

type. Most component types require different sub$-$component types.