Google, Microsoft and Yahoo! have decided to propose a common markup vocabulary, Schema.org, based on the Microdata format, simplifying the job of webmasters who want to give meaning to their web pages content.
Google has supported Microdata, Microformats, and RDFa so far, letting webmasters decide which markup format serves their interest best. Each markup format has its advantages, Microdata being the last to emerge in the semantic web by trying to combine the extensibility provided by RDFa and simplicity of microformats. Now, that seems to be changing since three major online companies, Google, Microsoft and Yahoo!, have agreed to propose a new common markup vocabulary under the Schema.org umbrella that Google’s search engine and Bing will use to create rich snippets for webpages. Schema.org relies on the Microdata format, a W3C HTML markup specification.
Schema.org has a rich vocabulary covering all the items defined by Microdata, Microformats, and RDFa so far, but all types are the subtypes of DataType and Thing, all defined using the following HTML attributes: itemscope, itemtype and itemprop. The following is a markup example of a Movie:
<div itemscope itemtype ="http://schema.org/Movie"> <h1 itemprop="name">Avatar</h1> <span>Director: <span itemprop="director">James Cameron</span> (born August 16, 1954)</span> <span itemprop="genre">Science fiction</span> <a href="../movies/avatar-theatrical-trailer.html" itemprop="trailer">Trailer</a> </div>
Google says they chose Microdata because they wanted to “focus on just one format” and “a single format will improve consistency across search engines relying on the data”. But, of course, the benefit for webmasters is the fact that one markup will work both with Google and Bing, they not having to provide separate markup for different search engines. It is expected the other search companies to adapt their engines to support Schema.org.
Google also says they will support existing Microformats and RDFs markups, so webmasters don’t have to change anything, but they are enticed to convert existing markup to Schema.org because it is recognized by Microsoft and Yahoo! beside Google.
Update. Schema.org mentiones they will perhaps support other formats in the future without specifying which ones: "While the long term goal is to support a wider range of formats, the initial focus is on Microdata.". Likely candidates are Microformats, and RDFa.
Schema.org has included an extension mechanism, allowing websites to create their own sub-vocabularies that are partially understood by Google and Bing, with the promise that the markup will be included in the root vocabulary if it receives wide adoption. This mechanism lets websites extend types or their properties.
Regarding Facebook Open Graph, another markup solution, Google says that Schema.org provides more detail for the entities contain by web pages, and Open Graph, while very well suited for what it does, it is somehow limited, so it is not the solution needed for search.
Google also provides a Rich Snippets Testing Tool that webmasters can use to test the markup of their pages.
