Microdata (HTML)

Microdata is a WHATWG HTML5 specification used to nest semantics within existing content on web pages.^[1] Search engines, web crawlers, and browsers can extract and process Microdata from a web page and use it to provide a richer browsing experience for users. Microdata use a supporting vocabulary to describe an item and name-value pairs to assign values to its properties.^[2] Microdata helps technologies such as search engines and web crawlers better understand what information is contained in a web page, providing better search results. Microdata is an attempt to provide a simpler way of annotating HTML elements with machine readable tags than the similar approaches of using RDFa and Microformats.

Microdata Vocabularies

Microdata vocabularies provide the semantics, or meaning of an Item. Web developers can design a custom vocabulary or use vocabularies available on the web. A collection of commonly used (and Google Supported^[3]) Microdata vocabularies located at http://data-vocabulary.org which include: Person, Event, Organization, Product, Review, Review-aggregate, Breadcrumb, Offer, Offer-aggregate. For some purposes, an ad-hoc vocabulary is adequate. For others, a vocabulary will need to be designed. Where possible, authors are encouraged to re-use existing vocabularies, as this makes content re-use easier.^[1]

Microdata Global Attributes

Itemscope – Creates the Item and indicates that descendants of this element contain information about it.^[1] This attribute precedes the itemtype attribute in the HTML element’s tag.
Itemtype – A valid URL of a vocabulary that describes the item and its properties context.
ItemId – Indicates a unique identifier of the item in the vocabulary.
Itemprop – Indicates that its containing tag holds the value of the specified item property. The properties name and value context are described by the items vocabulary. Properties values usually consist of string values, but can also use URL's using the a element and its href attribute, the img element and its src attribute, or other elements that link to or embed external resources.^[1]
Itemref - Properties that are not descendants of the element with the itemscope attribute can be associated with the item using this attribute. Provides a list of elements to web crawlers to find additional property values of the item elsewhere in the document.^[1]

Example

The following markup may be found on a typical about page containing information about a person:

<section> Hello, my name is John Doe, I am a graduate research assistant at the University of Dreams. My friends call me Johnny. 
You can visit my homepage at <a href="http://www.JohnnyD.com">www.JohnnyD.com</a>. I live at 1234 Peach Drive Warner Robins, Georgia.</section>

Here is the same markup with added Microdata:

<section itemscope itemtype="http://data-vocabulary.org/Person"> 
	Hello, my name is 
	<span itemprop="name">John Doe</span>, 
	I am a 
	<span itemprop="title">graduate research assistant</span> 
	at the 
	<span itemprop="affiliation">University of Dreams</span>. 
	My friends call me 
	<span itemprop="nickname">Johnny</span>. 
	You can visit my homepage at 
	<a href="http://www.JohnnyD.com" itemprop="url">www.JohnnyD.com</a>. 
	<section itemprop="address" itemscope itemtype="http://data-vocabulary.org/Address">
		I live at 
		<span itemprop="street-address">1234 Peach Drive</span> 
		<span itemprop="locality">Warner Robins</span>
		, 
		<span itemprop="region">Georgia</span>.
	</section>
</section>

As the above example shows, Microdata items can be nested. In this case an item of type http://data-vocabulary.org/Address is nested inside a item of type http://data-vocabulary.org/Person.

The following text shows how Google parses the Microdata from the above example code. Developers can test pages containing Microdata using Google's Rich Snippet Testing Tool.^[3]

Item
   Type: http://data-vocabulary.org/Person
   name = John Doe
   title = graduate research assistant
   affiliation = University of Dreams
   nickname = Johnny
   url = http://www.johnnyd.com/
   address = Item(1)
Item 1
   Type: http://data-vocabulary.org/Address
   street-address = 1234 Peach Drive
   locality = Warner Robins
   region = Georgia

Support

Google can use microdata in its result pages.^[3]

Currently, no browser supports the Microdata DOM API.

External links

Microdata — HTML5 Draft Standard, WHATWG
Almaer, Dion (2009-05-11), Hixie discusses the addition of HTML5 “microdata”, Ajaxian
HTML5 Microdata Specs, Data-Vocabulary.org

References

[WHATWG-1] Microdata — HTML5 Draft Standard

[DIVE-2] “Distributed,” “Extensibility,” And Other Fancy Words, Dive Into HTML5

[GoogleRS-3] Rich snippets (microdata, microformats, RDFa), Google webmaster central

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