xtrabackup 备份恢复测试过程

1.  

Microdata annotates the DOM
with scoped name/value pairs from custom vocabularies. Anyone can define a
microdata vocabulary and start embedding custom properties in their own web
pages. Microdata works with name/value pairs. Every microdata vocabulary
defines a set of named properties. Along with named properties, microdata
relies heavily on the concept of “scoping.” Microdata re-uses the hierarchical
structure of the DOM itself to provide a way to say “all the properties within this

element are taken from this

vocabulary.” You can even nest
microdata vocabularies within other vocabularies, all by re-using the natural
structure of the DOM. Microdata is a complement to HTML and works best for
fine-tuning the semantics of data that’s already in the DOM, but the HTML
vocabulary isn’t quite expressive enough. If the data you’re semanti-fying
isn’t in the DOM, you should step back and re-evaluate whether microdata is the
right solution.

 

 
2.  

To define your own microdata
vocabulary, first, you need a namespace, which is just a URL. The namespace URL
could actually point to a working web page, although that’s not strictly
required. A microdata property name is always declared on an HTML element. The
corresponding property value is then taken from the element’s DOM. For most
HTML elements, the property value is simply the text content of the element.
But there are a handful of exceptions:



“Text
content” doesn’t mean “all the markup inside this element” (like you would get
with, say, the

innerHTML

DOM property). It means “just the text”.

 
3.  

“Adding microdata” to your page
is a matter of adding a few attributes to the HTML elements you already have.
The first thing you always do is declare which microdata vocabulary you’re
using, by adding an itemtype

attribute. The second thing you always do is
declare the scope of the vocabulary, using an itemscope

attribute:

 

<section itemscope itemtype="http://data-vocabulary.org/Person">

<h1 itemprop="name">Mark Pilgrim</h1>

…

 
    
In English, this says
“here is the name property of the http://data-vocabulary.org/Person vocabulary,
and the value of the property is Mark Pilgrim.”

 
4.  

It’s a best practice to put
your documentation about the microdata vocabulary on the vocabulary URL itself.

 
5.  

Microdata doesn’t have a way to
break up runs of text into separate properties. You can’t say “the first 18
characters of this text is one microdata property, and the last 12 characters
of this text is another microdata property.”

 
6.  

A microdata property itself can
be a microdata item. That means we need to add the itemscope

and itemtype

attributes to the element too:

<section itemscope itemtype="http://data-vocabulary.org/Person">

…

<dt>Mailing address</dt>

<dd itemprop="address" itemscope itemtype="http://data-vocabulary.org/Address">

 
 

This is nested
scope — defining a new itemtype

and itemscope

(on the <dd>

element)
within an existing one (on the <section>

element). This nested scope
works exactly like the HTML
DOM
. The <dd>

element has a certain number of child elements, all of which are scoped to the
vocabulary defined on the <dd>

element. Once the <dd>

element is
closed with a corresponding </dd>

tag, the scope reverts to the
vocabulary defined by the parent element (<section>

, in this case).

 
7.  

Technically, any microdata property
can appear more than once.

 
8.  

There are two major classes of
applications that consume HTML, and by extension, HTML5 microdata:

  a)  

Web browsers

  b)  

Search engines

For
browsers, HTML5
defines a
set of DOM
APIs

for extracting microdata items,
properties, and property values from a web page. But no one support it. When
Google’s web crawler parses your page and finds microdata properties that
conform to the http://data-vocabulary.org/Person

vocabulary, it parses out
those properties and stores them alongside the rest of the page data. Google
even provides a
handy tool to see how Google “sees” your microdata properties
.