Microdata is a WHATWG HTML specification used to nest metadata within existing content on web pages. 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. Search engines benefit greatly from direct access to this structured data because it allows them to understand the information on web pages and provide more relevant results to users. Microdata uses a supporting vocabulary to describe an item and name-value pairs to assign values to its properties. 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.
In 2013, because the W3C HTML Working Group failed to find someone to serve as an editor for the Microdata HTML specification, its development was terminated with a 'Note'. However, since that time, two new editors were selected, and two newer versions of the working draft have been published, W3C First Public Working Draft 04 May 2017 and W3C Working Draft 26 June 2017.
Microdata vocabularies does not 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 markup vocabularies are provided by Schema.org schemas which include: Person, "Place", Event, Organization, Product, Review, Review-aggregate, Breadcrumb, Offer, Offer-aggregate. Major search engine operators like Google, Microsoft and Yahoo! rely on this markup to improve search results. 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.
In some cases, search engines covering specific regions may provide locally-specific extensions of microdata. For example, Yandex, a major search engine in Russia, supports microformats such as hCard (company contact information), hRecipe (food recipe), hReview (market reviews) and hProduct (product data) and provides its own format for definition of the terms and encyclopedic articles. This extension was made in order to solve transliteration problems between the Cyrillic and Latin alphabets. After the implementation of additional parameters from Schema's vocabulary, indexation of information in Russian-language web-pages became more successful.
itemscope– Creates the Item and indicates that descendants of this element contain information about it.
itemtype– A valid URL of a vocabulary that describes the item and its properties context.
itemid– Indicates a unique identifier of the item.
itemprop– Indicates that its containing tag holds the value of the specified item property. The property's name and value context are described by the item's vocabulary. Properties values usually consist of string values, but can also use URLs using the
aelement and its
imgelement and its
srcattribute, or other elements that link to or embed external resources.
itemref– Properties that are not descendants of the element with the
itemscopeattribute can be associated with the item using this attribute. Provides a list of element ids (not
itemids) with additional properties elsewhere in the document.
The following HTML5 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>
<section itemscope itemtype="http://schema.org/Person"> Hello, my name is <span itemprop="name">John Doe</span>, I am a <span itemprop="jobTitle">graduate research assistant</span> at the <span itemprop="affiliation">University of Dreams</span>. My friends call me <span itemprop="additionalName">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://schema.org/PostalAddress"> I live at <span itemprop="streetAddress">1234 Peach Drive</span>, <span itemprop="addressLocality">Warner Robins</span>, <span itemprop="addressRegion">Georgia</span>. </section> </section>
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.
Item Type: http://schema.org/Person name = John Doe jobTitle = graduate research assistant affiliation = University of Dreams additionalName = Johnny url = http://www.johnnyd.com/ address = Item(1) Item 1 Type: http://schema.org/PostalAddress streetAddress = 1234 Peach Drive addressLocality = Warner Robins addressRegion = Georgia
The same machine-readable terms can be used not only in HTML Microdata, but also in other annotations such as RDFa or JSON-LD in the markup, or in an external RDF file in a serialization such as RDF/XML, Notation3, or Turtle.
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