Google, Microsoft, and Yahoo have teamed up to encourage Web page operators to make the meaning of their pages understandable to search engines.

The three big Web companies launched the semantic-Web-technology initiative, known as Schema.org, last week. It defines an interconnected vocabulary of terms that can be added to the HTML markup of a Web page to communicate the meaning of concepts on the page. This data will allow search engines to better understand how useful a page may be for a given search query.

Schema.org asks for semantic markup to be written using a format known as microdata, which is not yet a W3C standard, rather than RDFa, a more widely used W3C-approved alternative.