XQuery Functions
--------------------------------------------------------------------------------
XQuery 1.0, XPath 2.0, and XSLT 2.0 share the same functions library.
--------------------------------------------------------------------------------
XQuery Functions
XQuery 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. You can also define your own functions in XQuery.
--------------------------------------------------------------------------------
XQuery Built-in Functions
The URI of the XQuery function namespace is:
http://www.w3.org/2005/02/xpath-functions
The default prefix for the function namespace is fn:.
Tip: Functions are often called with the fn: prefix, such as fn:string(). However, since fn: is the default prefix of the namespace, the function names do not need to be prefixed when called.
The reference of all the built-in XQuery 1.0 functions is located in our XPath tutorial.
--------------------------------------------------------------------------------
Examples of Function Calls
A call to a function can appear where an expression may appear. Look at the examples below:
Example 1: In an element
<name>{uppercase($booktitle)}</name>
Example 2: In the predicate of a path expression
doc("books.xml")/bookstore/book[substring(title,1,5)='Harry']
Example 3: In a let clause
let $name := (substring($booktitle,1,4))
--------------------------------------------------------------------------------
XQuery User-Defined Functions
If you cannot find the XQuery function you need, you can write your own.
User-defined functions can be defined in the query or in a separate library.
Syntax
declare function prefix:function_name($parameter AS datatype)
AS returnDatatype
{(: ...function code here... :)};
Notes on user-defined functions:
Use the declare function keyword
The name of the function must be prefixed
The data type of the parameters are mostly the same as the data types defined in XML Schema
The body of the function must be surrounded by curly braces
Example of a User-defined Function Declared in the Query
declare function local:minPrice(
$price as xs:decimal?,
$discount as xs:decimal?)
AS xs:decimal?
{
let $disc := ($price * $discount) div 100
return ($price - $disc)
};(: Below is an example of how to call the function above :)<minPrice>{local:minPrice($book/price, $book/discount)}</minPrice>
XQuery 函数
XQuery含有超过100个内建的函数。这些函数可用于字符串值、数值、日期以及时间比较、节点和QName操作、序列操作、逻辑值等等。您也可在XQuery中定义自己的函数。
XQuery 内建函数
XQuery函数命名空间的URI：
http://www.w3.org/2005/02/xpath-functions
函数命名空间的默认前缀是fn:。
提示：函数经常被通过fn:前缀进行调用，例如fn:string()。不过，由于fn:是命名空间的默认前缀，所以函数名称不必在被调用时使用前缀。
您可以在我们的XPath教程中找到完整的《内建XQuery函数参考手册》。
函数调用实例
函数调用可与表达式一同使用。请看下面的例子：
例1：在元素中
<name>{uppercase($booktitle)}</name>例2: 在路径表达式的谓语中
doc("books.xml")/bookstore/book[substring(title,1,5)='Harry']例3: 在let语句中
let $name := (substring($booktitle,1,4))XQuery 用户定义函数
如果找不到所需的XQuery函数，你可编写自己的函数。
可在查询中或独立的库中定义用户自定义函数。
语法
declare function 前缀:函数名($参数 AS 数据类型)
AS 返回的数据类型
{
(: ...函数代码... :)
};关于用户自定义函数的注释：
请使用declare function关键词
函数名须使用前缀
参数的数据类型通常与在XML Schema中定义的数据类型一致
函数主体须被花括号包围
一个在查询中声明的用户自定义函数的例子：
declare function local:minPrice(
$price as xs:decimal?,
$discount as xs:decimal?)
AS xs:decimal?
{
let $disc := ($price * $discount) div 100
return ($price - $disc)
};
(: Below is an example of how to call the function above :)
<minPrice>{local:minPrice($book/price, $book/discount)}</minPrice>
(注：这一块学了两遍，有点搞不清，直接抄了别人的翻译资料过来。再学学看！）
[此贴子已经被作者于2007-4-18 11:05:53编辑过]
[返回] W3CHINA.ORG讨论区 - 语义网·描述逻辑·本体·RDF·OWL →
XML.ORG.CN讨论区 - XML技术 → 『 XQuery/XLink/XPointer/ 』 → XQuery从头学
(订阅本版)
2007/4/12 15:33:00
新浪微博
XQuery从头学
