Indicates the Item Specific's logical dependency on another Item Specific, if any.
For example, in a clothing category, Size Type could be recommended as a parent of Size, because Size=XL would mean something different to buyers when Size Type=Juniors or Size Type=Regular.
Or in the US (in the future), a list of cities can vary depending on the state, so State could be recommended as a parent of City.
Currently, categories only recommend a maximum of one parent for an Item Specific. For example, Size=XL could have a Size Type=Juniors parent in a Juniors clothing category. In the future, some categories may recommend multiple parents. For example, City=Mountain View could have parents like State=California, State=New York, and State=North Carolina.
If an Item Specific has value dependencies (i.e., if it has value recommendations that contain Relationship), then all of its value recommendations are returned (regardless of the number you specified in MaxValuesPerName).
See the Field Index
to learn which calls use Relationship.