This ReferenceType can be used to expose the relation between a hardware component and its subcomponent. It indicates that the subcomponent is attached to the component. That implies that the subcomponent is located in direct contact or direct vicinity of the component and is visible from the outside of the component without removing parts of the component (like a hatch). For example, it can be used to relate a drive device or a modular IO-station which is composed out of a device head and multiple IO-modules attached to the head to such an IO-module like a fieldbus interface module. Another example is a laptop having a removable battery attached to it.