【转】XPath 语法

 

XPath is a language for finding information in an XML document. XPath is used to navigate through elements and attributes in an XML document.
Xpath 是一种能够在 XML 文档中寻找信息的语言。它通过 XML 文档中的元素和属性来进行导航。

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What You Should Already Know
你应具备的知识

Before you continue you should have a basic understanding of the following:
在你继续前你应该具备以下知识的基础：

·        HTML / XHTML

·        XML / XML Namespaces[ 命名空间 ]

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What is XPath?
什么是 XPath?

·        XPath is a syntax for defining parts of an XML document
XPath 是针对 XML 文档部分内容定义的语法

·        XPath uses path expressions to navigate in XML documents
XPath 使用路径表达式在 XML 文档中导航

·        XPath contains a library of standard functions
XPath 包含了一系列标准函数

·        XPath is a major element in XSLT
XPath 在 XSLT 当中是一个主要的元素

·        XPath is a W3C Standard
XPath 是 W3C 标准

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XPath Path Expressions
XPath 路径表达式

XPath uses path expressions to select nodes or node-sets in an XML document. These path expressions look very much like the expressions you see when you work with a traditional computer file system.
XPath 使用路径表达式来选择 XML 文档中的 nodes( 节 ) 或是 node-set( 节集 ) 。这些路径表达式看上去与你平时所见的传统计算机文件系统路径非常地相似。

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XPath Standard Functions
XPath 标准函数

XPath includes over 100 built-in functions. There are functions for string values, numeric values, date and time comparison, node and QName manipulation, sequence manipulation, Boolean values, and more.
XPath 包含了数量超过 100 的内置函数。这些函数针对字符串值，数字值，日期和时间比较，节操作，顺序操作，布尔值，等等。

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XPath is Used in XSLT
XPath 被用在 XSLT

XPath is a major element in the XSLT standard. Without XPath knowledge you will not be able to create XSLT documents.
在 XSLT 标准中 XPath 是主要的元素。没有 XPath 知识你将很难建立 XSLT 文档。

XQuery and XPointer are both built on XPath expressions. XQuery 1.0 and XPath 2.0 share the same data model and support the same functions and operators.
XQuery 和 XPointer 都建立于 XPath 表达式。 XQuery 1.0 和 XPath 2.0 共享相同的数据模型并支持相同的函数和操作

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XPath is a W3C Standard
XPath 是 W3C 标准

XPath became a W3C Recommendation 16. November 1999.
XPat 于 1999 年 11 月 16 日 成为 W3C 的推荐标准

XPath was designed to be used by XSLT, XPointer and other XML parsing software.
XPath 被设计成为用语 XSLT,XPoniter 以及其他 XML 解析的软件。

XPath Nodes( 节 )
翻译： Linyupark / 2006-03-24

In XPath, there are seven kinds of nodes: element, attribute, text, namespace, processing-instruction, comment, and document (root) nodes.
在 XPath 中有七种 nodes( 节 ) ：元素，属性，文字，命名空间，处理说明，注释，和文档 ( 根 ) 节。

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XPath Terminology
XPath 术语

Nodes/ 节

In XPath, there are seven kinds of nodes: element, attribute, text, namespace, processing-instruction, comment, and document (root) nodes. XML documents are treated as trees of nodes. The root of the tree is called the document node (or root node).
XML 文档被视为数状的节。树的根部被称为文档的节 ( 或根节 ) 。

Look at the following XML document:
观察下面的 XML 文档：

<?xml version="1.0" encoding="ISO-8859-1"?>

<bookstore>

<book>
 <title lang="en">Harry Potter</title>
 <author>J K. Rowling</author>
 <year>2005</year>
 <price>29.99</price>
</book>

</bookstore>

Example of nodes in the XML document above:
上面举例的 XML 文档的节有：

<bookstore> (document node)

<author>J K. Rowling</author> (element node)

lang="en" (attribute node)

Atomic values
原子值

Atomic values are nodes with no children or parent.
原子值是那些没有子或父的节（无上下关系）。

Example of atomic values:
举例中的原子值：

J K. Rowling

"en"

Items
项目

Items are atomic values or nodes.
项目是原子值或节。

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Relationship of Nodes
节之间的关系

Parent/ 父

Each element and attribute has one parent.
每个元素和属性有一父亲。

In the following example; the book element is the parent of the title, author, year, and price:
下面的举例中： book 元素是 title ， author ， year 和 price 的父亲

<book>
 <title>Harry Potter</title>
 <author>J K. Rowling</author>
 <year>2005</year>
 <price>29.99</price>
</book>

Children/ 子

Element nodes may have zero, one or more children.
元素节可能有 0 个或多个子

In the following example; the title, author, year, and price elements are all children of the book element:
下面的举例中： title,author,year 和 price 元素都是 book 元素的子元素

<book>
 <title>Harry Potter</title>
 <author>J K. Rowling</author>
 <year>2005</year>
 <price>29.99</price>
</book>

Siblings/ 兄

Nodes that have the same parent.
指那些有相同父的

In the following example; the title, author, year, and price elements are all siblings:
下面的举例中 title, author, year, 和 price 元素都为兄弟

<book>
 <title>Harry Potter</title>
 <author>J K. Rowling</author>
 <year>2005</year>
 <price>29.99</price>
</book>

Ancestors/ 祖

A node's parent, parent's parent, etc.
节的父，父的父 .... 都为祖

In the following example; the ancestors of the title element are the book element and the bookstore element:
下面的举例中： book 元素和 bookstore 元素都为 title 元素的祖元素

<bookstore>

<book>
 <title>Harry Potter</title>
 <author>J K. Rowling</author>
 <year>2005</year>
 <price>29.99</price>
</book>

</bookstore>

Descendants/ 孙

A node's children, children's children, etc.
节的子，子的子 ... 都为孙

In the following example; descendants of the bookstore element are the book, title, author, year, and price elements:
下面的举例中： bookstore 元素的孙有 book,title,author,year 以及 price 元素

<bookstore>

<book>
 <title>Harry Potter</title>
 <author>J K. Rowling</author>
 <year>2005</year>
 <price>29.99</price>
</book>

</bookstore>

 

XPath 语法
翻译： Linyupark / 2006-03-24

XPath uses path expressions to select nodes or node-sets in an XML document. The node is selected by following a path or steps.
XPath 使用路径表达式来选择 XML 文档的节或是节集。顺着路径或步骤来选择节。

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The XML Example Document
XML 实例文档

We will use the following XML document in the examples below.
举例中我们将使用下面的 XML 文档

<?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>

 

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Selecting Nodes
选择节

XPath uses path expressions to select nodes in an XML document. The node is selected by following a path or steps. The most useful path expressions are listed below:
一些非常有用的路径表达式：

表达式	描述
nodename	Selects all child nodes of the node[ 选择所有目前节的子节 ]
/	Selects from the root node[ 从根节进行选择 ]
//	Selects nodes in the document from the current node that match the selection no matter where they are [ 选择文档中相吻合的节而不管其在文档的何处 ]
.	Selects the current node[ 选择当前节 ]
..	Selects the parent of the current node[ 当前节的父节 ]
@	Selects attributes[ 选择属性 ]

Examples
实例

In the table below we have listed some path expressions and the result of the expressions:
下面我们所列举的表格有路径表达式以及其结果：

路径表达式	结果
bookstore	Selects all the child nodes of the bookstore element[ 选择所有 bookstore 元素的子节 ]
/bookstore	Selects the root element bookstore Note: If the path starts with a slash ( / ) it always represents an absolute path to an element! [ 选择了 bookstore 的根元素。注意：如果路径的开始为 (/) 那此路径一定是到该元素的绝对路径 ]
bookstore/book	Selects all book elements that are children of bookstore[ 选择了所有在 bookstore 的子元素 book 元素所包含的所有元素（其实就为 bookstore 里 book 元素所包含的元素） ]
//book	Selects all book elements no matter where they are in the document[ 选择所有为 book 元素的内容而不管 book 元素处于何处 ( 有不同的父也没关系 )]
bookstore//book	Selects all book elements that are descendant of the bookstore element, no matter where they are under the bookstore element[ 在 bookstore 元素内所有含有 book 元素的元素内容（只要 book 元素的祖元素为 bookstore 元素那都符合条件） ]
//@lang	Selects all attributes that are named lang[ 选择所有属性名为 lang 的属性 ]

 

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Predicates
谓语

Predicates are used to find a specific node or a node that contains a specific value.
谓语用来指定明确的节所含有的特殊的值

Predicates are always embedded in square brackets.
谓语被嵌入在中括号

Examples
举例

In the table below we have listed some path expressions with predicates and the result of the expressions:
下面的表格列举了一些使用了谓语的路径表达式以及其产生的结果：

路径表达式	结果
/bookstore/book[1]	Selects the first book element that is the child of the bookstore element[ 选择了 bookstore 里的第一个 book 元素 ]
/bookstore/book[last()]	Selects the last book element that is the child of the bookstore element[ 选择 bookstore 里最后一个 book 元素 ]
/bookstore/book[last()-1]	Selects the last but one book element that is the child of the bookstore element[bookstore 中倒数第二个 book 元素 ]
/bookstore/book[position()<3]	Selects the first two book elements that are children of the bookstore element[ 在 bookstore 中前两个 book 元素 ]
//title[@lang]	Selects all the title elements that have an attribute named lang[ 选择所有含有 lang 属性的 title 元素 ]
//title[@lang='eng']	Selects all the title elements that have an attribute named lang with a value of 'eng'[ 选择所有含有 lang 属性并且值为 eng 的 title 元素 ]
/bookstore/book[price>35.00]	Selects all the book elements of the bookstore element that have a price element with a value greater than 35.00[ 选择所有 bookstore 中 book 元素里 price 元素内容大于 35.00 的 book 元素 ]
/bookstore/book[price>35.00]/title	Selects all the title elements of the book elements of the bookstore element that have a price element with a value greater than 35.00[ 选择 bookstore 中 book 的子元素 title ，并且其兄弟元素 price 的内容得大于 35.00]

 

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Selecting Unknown Nodes
选择未知的节

XPath wildcards can be used to select unknown XML elements.
XPath 的通配符可以用来选择未知的 XML 元素

通配符	描述
*	Matches any element node[ 相吻合的所有元素节 ]
@*	Matches any attribute node[ 相吻合的所有属性节 ]
node()	Matches any node of any kind[ 吻合任何类型的节 ]

Examples 实例

In the table below we have listed some path expressions and the result of the expressions:
下面的表格我们将列举一些路径表达式以及它们的结果

路径表达式	结果
/bookstore/*	Selects all the child nodes of the bookstore element[ 选择所有 bookstore 的子节 ]
//*	Selects all elements in the document[ 选择所有文档中的元素 ]
//title[@*]	Selects all title elements which have any attribute[ 选择元素为 title 并且其含有属性 ]

 

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Selecting Several Paths

 

选择数个路径

By using the | operator in an XPath expression you can select several paths.
通过在 XPath 中使用 | 你可以选择数个路径

Examples
实例

In the table below we have listed some path expressions and the result of the expressions:
下面的表格我们会列举一些路径表达式以及其结果：

路径表达	结果
//book/title | //book/price	Selects all the title AND price elements of all book elements[ 选择所有 book 里 title 和 price 元素 ]
//title | //price	Selects all the title AND price elements in the document[ 选择所有 title 和 price 元素 ]
/bookstore/book/title | //price	Selects all the title elements of the book element of the bookstore element AND all the price elements in the document[ 选择所有 book 里的 title 元素和所有 price 元素 ]

 

XPath 轴
翻译： Linyupark / 2006-03-24