The upper two trees on the left are endocentric since each time, one of the parts, i.e. the head, projects its category status up to the mother node. The upper tree on the right, in contrast, is exocentric, because neither of the parts projects its category status up to the mother node; Z is a category distinct from X or Y. The two dependency trees show the manner in which dependency-based structures are inherently endocentric. Since the number of nodes in the tree structure is necessarily equal to the number of elements (e.g. words) in the string, there is no way to assign the whole (i.e. XY) a category status that is distinct from both X and Y.