XPath Axes Basic

The XML Example Document

We will use the following XML document in the examples below.

<?xml version="1.0" encoding="ISO-8859-1"?>
<bookstore>
  <book>
    <title lang="eng">Harry Potter</title>
    <price>29.99</price>
  </book>
  <book>
    <title lang="eng">Learning XML</title>
    <price>39.95</price>
  </book>
</bookstore>

XPath Axes

An axis defines a node-set relative to the current node.

一条主线指定了一系列的节点和当前节点的关系

AxisName	Result
ancestor	Selects all ancestors (parent, grandparent, etc.) of the current node 选择当前节点的所有的祖先，根，（父，父之父）
ancestor-or-self	Selects all ancestors (parent, grandparent, etc.) of the current node and the current node itself 选择当前节点所有的祖节点和自己
attribute	Selects all attributes of the current node 选择当前节点的所有属性
child	Selects all children of the current node 选择当前节点的所有子节点
descendant	Selects all descendants (children, grandchildren, etc.) of the current node 选择当前节点的所有胄（子，子之子等）
descendant-or-self	Selects all descendants (children, grandchildren, etc.) of the current node and the current node itself 选择当前节点的所有子节点和自己
following	Selects everything in the document after the closing tag of the current node 选择当前节点结束后的文档中的所有节点
following-sibling	Selects all siblings after the current node 选择当前节点后的所有同科节点
namespace	Selects all namespace nodes of the current node 选择当前节点的所有的名字空间
parent	Selects the parent of the current node 选择当前节点的所有父节点
preceding	Selects everything in the document that is before the start tag of the current node 选择文档中当前节点前的所有节点
preceding-sibling	Selects all siblings before the current node 选择当前节点前的所有同科节点
self	Selects the current node 选择当前节点

Location Path Expression位置表达式

A location path can be absolute or relative.

可以是绝对的也可以是相对的

An absolute location path starts with a slash ( / ) and a relative location path does not. In both cases the location path consists of one or more steps, each separated by a slash:

一个绝对的路径以＂／＂开始，两种表示式都有一级或多级构成，级用＂／＂分开

An absolute location path:

/step/step/...

A relative location path:

step/step/...

Each step is evaluated against the nodes in the current node-set.

每一级都是根据当前节点的在节点集的位置来执行的

A step consists of:级构成：

an axis (defines the tree-relationship between the selected nodes and the current node) 主线（规定一个当前节点和所先节点的关系树）
a node-test (identifies a node within an axis) 一个节点测试（在主线中辨认一个节点）
zero or more predicates (to further refine the selected node-set) 一个或多个谓词（进一步挑选选定的节点集）

The syntax for a location step is:语法

axisname::nodetest[predicate]

Examples:

Example	Result
child::book	Selects all book nodes that are children of the current node 选择当前节点的所有的book节点
attribute::lang	Selects the lang attribute of the current node 选择当前节点的lang 属性
child::*	Selects all children of the current node 选择当前节点的所有子节点
attribute::*	Selects all attributes of the current node 选择当前节点的所有属性
child::text()	Selects all text child nodes of the current node 选择当前节点的所有文本子节点
child::node()	Selects all child nodes of the current node 选择当前节点的所有子节点
descendant::book	Selects all book descendants of the current node 选择当节点的所有book胄
ancestor::book	Selects all book ancestors of the current node 选择当前节点的所有book节点的祖，根
ancestor-or-self::book	Selects all book ancestors of the current node - and the current as well if it is a book node 选择当前节点的book元素的根节点或它自己（如果它也是一个book节点的话）
child::*/child::price	Selects all price grandchildren of the current node