Components can have an installation relationship with other components.

A component which is installed in another component is a subcomponent. Note that this relation is not time-related, unlike the hierarchy of systems it does not reflect historical changes.
The actual reference of components and subcomponents to a system must be consistent, which means that a subcomponent is normally expected to be assigned to the same system as its superior component. There is, however, an option to keep the component hierarchy and the reference of the component to a system separate. (Check box Subcomponents Spanning System in system configuration).

The hierarchy of components can be predefined by the relation between product type and components type (Product Type Assignment To Component Type), in which case new components created during the Create Component out of Incoming Goods action are assembled in the desired predefined hierarchy. During the process, the predefined hierarchy can be changed for individual components.

For existing components, the hierarchy can be changed either manually in the component editor (changing the links to supercomponent or subcomponents) or in system configuration.

Note: When it comes to "installation", we intuitively distinguish between "installation" with or without a screwdriver.

• Installation with a screwdriver: a PCI expansion card, a hardrive, etc.

  This installation relationship is modeled using component relations.

• Installation without a screwdriver: e.g. connecting/installing a printer to a PC

  This installation relationship is not modeled but it is reflected in the relationship between systems.