The Oxford English Dictionary records use of both the terms "tree structure" and "tree-diagram" from 1965 in Noam Chomsky's Aspects of the Theory of Syntax. Tree structures can depict all kinds of taxonomic knowledge, such as family trees, the biological evolutionary tree, the evolutionary tree of a language family, the grammatical structure of a language (a key example being S → NP VP, meaning a sentence is a noun phrase and a verb phrase, with each in turn having other components which have other components), the way web pages are logically ordered in a web site, mathematical trees of integer sets, et cetera. Finally, "science", "art" and "craft", as leaves, are ancestors of no other node. Also, "encyclopedia", as the root of the tree, is the ancestor of "science", "culture", "art" and "craft". "Art" and "craft" are siblings, and children of "culture", which is their parent and thus one of their ancestors. In the example, "encyclopedia" is the parent of "science" and "culture", its children. The connected lower-level nodes are "descendants" of the ancestor node. A node that is connected to all lower-level nodes is called an "ancestor".A node's "uncles" (sometimes "ommers") are siblings of that node's parent."Sibling" ("brother" or "sister") nodes share the same parent node.closer to the root node) and lying on the same branch. A node's "parent" is a node one step higher in the hierarchy (i.e.The term "uncle" is still widely used for other nodes at the same level as the parent, although it is sometimes replaced with gender-neutral terms like "ommer". The gender-neutral names "parent" and "child" have largely displaced the older "father" and "son" terminology. The names of relationships between nodes model the kinship terminology of family relations. But the converse is not true: infinite tree structures may or may not have a root node. This member is called the "root" or root node. Nodes without children are called leaf nodes, "end-nodes", or "leaves".Įvery finite tree structure has a member that has no superior. The lines connecting elements are called "branches". For a discussion of tree structures in specific fields, see Tree (data structure) for computer science insofar as it relates to graph theory, see tree (graph theory) or tree (set theory). It is named a "tree structure" because the classic representation resembles a tree, although the chart is generally upside down compared to a biological tree, with the "stem" at the top and the "leaves" at the bottom.Ī tree structure is conceptual, and appears in several forms. ( July 2014) ( Learn how and when to remove this template message)Ī tree structure showing the possible hierarchical organization of an encyclopedia The original Encyclopédie (1752) used a tree diagram to show the way in which its subjects were ordered.Ī tree structure, tree diagram, or tree model is a way of representing the hierarchical nature of a structure in a graphical form. Please help to improve this article by introducing more precise citations. This article includes a list of general references, but it lacks sufficient corresponding inline citations.
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