## Quick Reference

*n*≥0 disjoint sets, *T*_{1}, *T*_{2},…, *T** _{n}*, where each of these sets is itself a tree. The sets

*T*

_{1},

*T*

_{2},…,

*T*

*are called subtrees of the root. If the order of these subtrees is significant, the tree is called an ordered tree, otherwise it is sometimes called an unordered tree.*

_{n}A tree corresponds to a graph with the root node matching a vertex connected by (directed) arcs to the vertices, which match the root nodes of each of its subtrees. An alternative definition of a (**directed**) tree can thus be given in terms from graph theory: a tree is a directed acyclic graph such that firstly there is a unique vertex, which no arcs enter, called the root, secondly every other vertex has exactly one arc entering it, and thirdly there is a unique path from the root to any vertex.

The diagram shows different representations of a tree.

The terminology associated with trees is either of a botanic nature, as with forest, leaf, root, or is genealogical, as with ancestor, descendant, child, parent, sibling. See also binary tree.

**Tree.**Sample tree represented as a Venn diagram (top) and as a directed graph

**From:**
tree
in
A Dictionary of Computing »

*Subjects:*
Computing.

## Related content in Oxford Index

##### Reference entries

Users without a subscription are not able to see the full content. Please, subscribe or login to access all content.