Leaf nodes, parent nodes and root nodes associate with each other one to one, with specific pairs of classes having specific relations. For example, Table I [Figure omitted. See Article Image.], depicts the relation between the classes Author and Paper Title as "write", meaning that someone writes a paper. The Feature field of this relation is "inverse", which means that the relation between the classes is reversible.
Saha, J. K., Selladurai, R., Coumar, M. V., Dotaniya, M. L., Kundu, S., & Patra, A. K. (2017). Soil Pollution - An Emerging Threat to Agriculture (Vol. 10, p. 386). Springer Singapore. https://doi.org/10.1007/978-981-10-4274-4