Microdata are additional markups for a type of information within HTML documents, Atom, RSS feeds, as well as XML files. Microdata flag specific information by stating something about the element described.
This is done by specifying certain properties that are specified in the respective micro-format. A property consists of a name-value pair. A set of properties is described as an item. Types of information such as people, places, events, assessments or stores can be identified that way.
Microdata is supported by HTML5 and can be integrated in the source code by using certain attributes. Other names for microdata is structured data or semantic HTML. However, microdata is not a particular format of this kind of markup, but rather the overall term for it. RDFa, scheme or individual micro-formats such as HCard, hProduct, hReview or Geo can be classified under the same topic, but should be considered syntactic variants. The aim is to identify data so that both search engines and users get an indication of its importance.
The micro-format HCard may be used on a website, for example, to display someone’s business card. Thus, properties such as name, street, postcode, place, and different contact options are listed and displayed accordingly. HCards may also be used for companies and organizations. In HTML5 a business card is referred to as a person and in some cases the difference between microdata and microformats must be observed, even if these formats are compatible.
The decisive advantage of microdata is the description of semantic information, i.e. information about what the respective data mean. Microformats are therefore one of many steps towards a semantic web in which the meaning of data is represented in various ways. Nevertheless, one should be consistent with the markup of data and only use one micro-format or specification.
Below is an example of markup with microdata in HTML source code. The person, Michael Smith, will be described with a set of name-value pairs. Before using these properties, they must be assigned a type. This is done with itemtype. Itemscope in turn indicates that a bundle of information follows, which is included by the div tag. The person format can also be used to represent HCard and vCard information.
<div itemscope itemtype="http://data-vocabulary.org/Person">My name is <span itemprop="name">Michael Smith</span>, my nickname is <span itemprop="nickname">Mike</span>. My website is: <a href="http://www.example.com" itemprop="url">www.example.com</a>. I live at <span itemprop="address" itemscope itemtype="http://data-vocabulary.org/Address"> <span itemprop="locality">Boston</span> in <span itemprop="region">Massachusetts</span> </span> and work as a<span itemprop="title">engineer</span>at<span itemprop="affiliation">Smith & Co.</span>. </div>
Microdata represent not only new data markup options, but have also been used in search engine optimization for some time. The Rel tag is an example. While Rel-nofollow is used to distance yourself from third-party content, Rel-author has been recently used to characterize the content creator.
Strictly speaking, these are also micro-formats and their relevance is not to be underestimated in the field of SEO. In particular, the authorship markup gained in importance recently, although now the author of a document is no longer displayed with photo in the search results.
Additionally, various micro-formats represent machine-readable content and thereby provide search engines with important information about the content. This may have the side effect that some types of information will be displayed in a special way in the SERPs and thus can increase the CTR.