The additional facet is defined in the metadata extension of the parent entity. The first facet, which was already there, displays the data of the parent entity itself. It is of type #IDENTIFICATION_REFERENCE.

 

The facet for the child entity data has to be of type #LINEITEM_REFERENCE. Facets of this type require a value for subannotation targetElement. Here, you specify the name of the association that links the child entity to the parent entity. Most of the time, this association will be a composition, or, more precisely, an association that is redirected to a composition child.