使用XML前缀/命名空间创建Xpath

问题描述

这是我的先前问题的后续文章.我想我跳到了最深层次，所以花了一些时间来充分了解XML名称空间.

来自此 XML页面，将重点放在下面的元素上一分钟:

<m:properties xmlns:m="http://schemas.microsoft.com/ado/2007/08/dataservices/metadata">

我知道使用m:前缀是为了将properties元素与其他文档中具有相同名称的元素区分开，以防合并此类文档.我知道要使用前缀，必须为该前缀定义一个名称空间.这样的定义是使用XML名称空间属性(xmlns)完成的，语法为xmlns:prefix="URI". URI是统一资源标识符，它基本上是元素的来源. URI以前称为统一资源名称(URN)，基本上是同一回事. /p>

现在看看我之前的问题的答案:

$url = "http://www.treasury.gov/resource-center/data-chart-center/interest-rates/pages/XmlView.aspx?data=yieldyear&year=2015";
$element = simplexml_load_file($url);

$element->registerXPathNamespace(
  'atom', 'http://www.w3.org/2005/Atom'
);
$element->registerXpathNamespace(
  'meta', 'http://schemas.microsoft.com/ado/2007/08/dataservice/metadata'
);

foreach ($element->xpath('//atom:entry/atom:content/meta:properties') as $properties) {
  $properties->registerXpathNamespace('data', 'http://schemas.microsoft.com/ado/2007/08/dataservices');
  echo $properties->xpath('data:Id')[0], "\n";
  echo $properties->xpath('data:NEW_DATE')[0], "\n\n";
}

XPath是用于定义XML文档各部分的语法. registerXPathNamespace()函数为指定的名称空间创建前缀.

对于我来说，为什么atom前缀是使用registerXPathNamespace() for <entry xmlns="http://www.w3.org/2005/Atom">创建的，以便像这样//atom:entry/atom:content/meta:properties一样引用它，这是因为入口标记未使用前缀.

为什么创建了meta前缀?已经有一个m:前缀，并且定义了相同的名称空间.

使用以下内容会做同样的事情吗?

//atom:entry/atom:content/m:properties

不幸的是，直到今天晚些时候我才可以访问我的服务器.那我自己测试一下.如果它不起作用，那么对为什么不感兴趣，逻辑会建议它应该这样做?

解决方案

在XML实例中绑定了m:前缀，但是您的XPath处理器不知道这一点.它需要单独绑定(注册)前缀.

meta:前缀是任意的.就像XML一样，它可能是m:，但这并不重要.只要URI相同即可. atom:前缀可能是a:，并且仍然可以使用.

This is a follow on from my prior question. I think I jumped in at the deep end so spending some time fully understanding XML namespaces.

From this XML page, gonna focus on the below element for a min:

<m:properties xmlns:m="http://schemas.microsoft.com/ado/2007/08/dataservices/metadata">

I understand that the m: prefix has been used in order to distinguish the properties element from elements with the same name in other documents, in case such documents are combined.I understand that in order to use a prefix, a namespace for that prefix must be defined. Such a definition is done using the XML namespace attribute (xmlns) and the syntax is xmlns:prefix="URI". URI is the Uniform Resource Identifier, which is basically the element's source. URIs used to be called Uniform Resource Names (URN), which are essentially the same thing.

Now taking a look at the answer to my prior Q:

$url = "http://www.treasury.gov/resource-center/data-chart-center/interest-rates/pages/XmlView.aspx?data=yieldyear&year=2015";
$element = simplexml_load_file($url);

$element->registerXPathNamespace(
  'atom', 'http://www.w3.org/2005/Atom'
);
$element->registerXpathNamespace(
  'meta', 'http://schemas.microsoft.com/ado/2007/08/dataservice/metadata'
);

foreach ($element->xpath('//atom:entry/atom:content/meta:properties') as $properties) {
  $properties->registerXpathNamespace('data', 'http://schemas.microsoft.com/ado/2007/08/dataservices');
  echo $properties->xpath('data:Id')[0], "\n";
  echo $properties->xpath('data:NEW_DATE')[0], "\n\n";
}

XPath is a syntax for defining parts of an XML document. The registerXPathNamespace() function creates a prefix for a specified namespace.

It makes sense to me why the atom prefix was created using registerXPathNamespace() for <entry xmlns="http://www.w3.org/2005/Atom"> in order to reference it like this //atom:entry/atom:content/meta:properties because the entry tag doesn't use a prefix.

Why was the meta prefix created? There was already an m: prefix with the same namespace defined.

Would using the below have done the same thing?

//atom:entry/atom:content/m:properties

Unfortunately, I don't have access to my server until later today. I'll test it myself then. If it doesn't work, more interested in why not, logic would suggest it should?

解决方案

The m: prefix was bound in the XML instance, but your XPath processor doesn't know that. It needs the prefix bound (registered) separately.

The meta: prefix is arbitrary. It could've been m: just like the XML, but it doesn't matter. As long as the URI is the same. The atom: prefix could've been a: and it would still work.

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