If you haven’t heard of Open Graph, you’ve at least heard of the system Facebook is implementing in some context, or seen an unusual message upon logging in to Facebook.

It depends. RDF is a graph data model that has been around since 1997. It's a W3C standard, and it's used to power schema.org and Open Graph, among other things.

Og:title is part of the Open Graph protocol, a set of meta tags developed by Facebook that allows any page to become a rich object in social graphs. While it’s used to control how content ...