In a rare display of collaboration, Google has joined forces with its search rivals Microsoft and Yahoo in a project intended to improve the Web crawling and indexing of structured data, which often originates in databases and loses its format when converted into HTML.

The three companies have launched a site called Schema.org, which contains a common set of HTML tags that they hope webmasters will use to mark up structured data on their sites.

"Schema.org aims to be a one stop resource for webmasters looking to add markup to their pages to help search engines better understand their websites," Google said in a blog post.

By promoting the use of these common tags across the Web, Yahoo, Microsoft and Google expect that their search engines will be better able to identify, crawl and index structured data.

"Many applications, especially search engines, can benefit greatly from direct access to this structured data. On-page markup enables search engines to understand the information on web pages and provide richer search results," reads a message in Schema.org's home page.

Schema.org contains more than 100 different HTML tags for structured data categories like events, organizations, people, places, products, reviews, ratings, movies and books.

Yahoo's SearchMonkey developer program was the first broadly popular search program designed to encourage webmasters to improve structured data markup on their sites, said IDC analyst Hadley Reynolds.

When Yahoo discontinued SearchMonkey last year, the search industry suffered a serious loss, so it's encouraging to see the main three search providers band together on this issue of structured data, he said via e-mail.

"As website managers add markup corresponding to the new 'catalog' of schemas published by [the three companies], it will make it much easier for the big three search sites to render the kind of enriched interaction metaphors which are proving to be the next phase of the competition between them for web searcher audiences," Reynolds said.

"The new program catches some of the spirit of SearchMonkey, while adding real value by including Google and Microsoft. This will now be a 'job one' for web developers looking to get their sites highly ranked by the [companies'] engines," he added.