Constituents have a parent feature, one that may be made mandatory. But the constituents list on PhraseStructure can also contain Tokens, which do not have a parent attribute. I see only ugly solutions: (1) add a parent feature to Token, (2) live with the fact that some elements in a tree have no parent, (3) let Token inherit from an element that has a parent feature, (4) use Constituents as leaf nodes, in which case we have no label and an empty children list, but we would have to add something like targets to refer to the Token and that means making Constituent a Region rather than a Relation.
The current situation is that we are following option 2.
This was first brought up in https://github.com/lapps/vocabulary-pages/issues/26, but I made it a separate issue so it does not get buried.
Constituents have a parent feature, one that may be made mandatory. But the constituents list on PhraseStructure can also contain Tokens, which do not have a parent attribute. I see only ugly solutions: (1) add a parent feature to Token, (2) live with the fact that some elements in a tree have no parent, (3) let Token inherit from an element that has a parent feature, (4) use Constituents as leaf nodes, in which case we have no label and an empty children list, but we would have to add something like targets to refer to the Token and that means making Constituent a Region rather than a Relation.
The current situation is that we are following option 2.