Tree

树，树形

(1) A two-dimensional diagram used in generative grammar as a convenient means of displaying the internal hierarchical structure of sentences as generated by a set of rules. The ‘root’ of the tree diagram is at the top of the diagram, consisting of the initial symbol S. From this topmost point, or node, branches descend corresponding to the categories specified by the rules (e.g. NP, VP). The internal relationships of parts of the tree are described using ‘family tree’ terminology: if two categories both derive from a single node, they are said to be ‘sisters’, and ‘daughters’ of the ‘mother node’ from which they derive. A subsection of a tree diagram, isolated for purposes of discussion, is referred to as a subtree, as in the enclosed area within the diagram below. The internal organization of a tree is sometimes referred to as tree geometry. In generalized phrase-structure grammar, the term local tree refers to a tree of depth one, i.e. a tree in which every node other than the root is a daughter of the root. The S-NP-VP subtree in the diagram below would be a local tree, in this context. In procedural grammar, a structure tree or parse tree is the result of applying the analytical procedures to a text. In computer corpus research, a parsed corpus is known as a treebank.

(2) In historical linguistics, a representation of the genetic relationships between the members of a family of languages.

（1）生成语法采用的一种二维图形，能方便的展示由一组规则生成的句子的内部层级结构。树形图的“根”在图形顶部，为起始符号S。从这个顶点或节点出发，往下的分叉对应于规则指定的各个语类（例如NP，VP）。树内各部分的关系用“谱系树”的术语来描写：如果两个语类从同一节点派生而来则构成“姐妹”节点；“子”节点从“母节点”派生而来。为单独论述而划出的树形图的一部分称作次树，如下图中框出的部分。树的内部组织有时称作树构架。在概化短语结构语法中，局部树是深度有限的树，即树中除根节点以外的每个节点都是根节点的子节点。如下图中的S-NP-VP次树就是这种涵义上的局部树。在程序语法中，结构树或分解树是对一篇章应用分析程序后得出的结果。在计算机语料库研究中，一个经分解的语料库称作树库。

（2）历史语言学中，一个语系的成员之间的谱系关系也用树来表示。