RDFa (or Resource Description Framework – in – attributes) is a W3C recommendation that adds a set of attribute level extensions to XHTML for embedding rich metadata within Web documents. This metadata protocol (RDFa) is used by the open graph protocol to enable any web page to become a rich object in a social graph. Facebook uses the open graph protocol to to make any web page look like facebook's pages. Example of properties defined in the open graph protocol are (Refer http://opengraphprotocol.org/ for more details):

• og:title - The title of your object as it should appear within the graph, e.g., "The Rock".
• og:type - The type of your object, e.g., "movie". Depending on the type you specify, other properties may also be required.
• og:image - An image URL which should represent your object within the graph.
• og:url - The canonical URL of your object that will be used as its permanent ID in the graph, e.g., "http://www.imdb.com/title/tt0117500/".

Great - so what about it? Recently Dries Buytaert gave his keynote at DrupalCon (which I highly recommend watching) and laid out the support for open graph protocol in Drupal 7. Meaning that Drupal 7 will inherently support RDF. Here is an update on the progress of this feature in Drupal 7. Facebook CEO Mark Zuckerberg also announced his support for open graph protocol in Facebook. 10s of thousands of website have converted their sites to also publish data in open graph protocol using RDF. Essentially all this makes sense if you also read the post which talks about Facebook search strategy. Facebook will compete with Google in the search market. The sites that implement the open graph protocol to publish data have inherent advantage of being indexed, searched and presented along with Facebook search results. This is huge for websites, since users can 'like' a site or 'comment' on a site like they do to native Facebook objects. The websites would get a lot direct feedback. This would also make the search results more relevant over time since there is a significant user input. This will give facebook a Semantic search engine enriched by inputs from its 100s of millions of users. And to Drupal websites an easy hook to leverage this move seamlessly to their advantage.