What is RDFa + microdata / microformats and why might I need them?

Question

I have stumbled upon RDFa and have seen the terms microdata and microformats used frequently.

What are they and why might they be useful when developing websites?

Answer 1

Semantics. Nowadays, the main reason is so Google can show Rich Snippets. To see how this works, put your page into http://www.google.com/webmasters/tools/richsnippets and see what it picks up. Try the examples on that page to see what they are using in search results.

Google also have a page called http://schema.org/ that outlines their microdata schema for marking things up.

In my opinion microdata is the way to go, microformats overloaded the class attribute, and though I understand it's within the spec, for me it's no longer the best place to put this info. RDFa is really good, but it's complex and not that obvious to most. Microdata is clear, well defined and backed by Google, hence my recommendation to use that.

On my sites, I've completely replace microformats with microdata, despite being a super early adopter and follower of the whole microformat system.