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the [Evolutionary tree |
In terms of graph theory, a tree can be described as a "directed acyclic graph". A collection of unconnected tree structures is sometimes described by graph theorists as a "forest". |
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A '''tree structure''' is a way of representing the [[hierarchy|hierarchical]] nature of a [[structure]] in a graphical form. It is named a 'tree structure', because the graph looks a bit like a tree, even though the tree is generally shown upside down compared with a real tree, that is to say with the root at the top and the leaves at the bottom.
In terms of [[graph]] theory, a tree can be described as a "directed acyclic graph". A collection of unconnected tree structures is sometimes described by graph theorists as a "forest".
<div style="width: 302px; float: right;">[[Image:binary-tree-structure.png]]<br>''Illustration: A tree structure showing the possible hierarchical organization of an encyclopedia. This specific example happens to a [[binary tree]], which means all nodes have exactly zero or two child nodes.''</div>
The lines connecting elements are called ''branches'', the elements themselves are called ''[[node|nodes]]''. Nodes without children are called ''end-nodes'' or ''leaves''.
The names of relationships between nodes are modelled after family relations. In computer sciences, traditionally only names for male family members have been used. In linguistics, the names of female family members are used. It is said that this was an express counter movement to the traditional naming convention, started by the female students of linguist [[Noam Chomsky]].
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