kryogenix has a comment about links between other places and says:

"I remain unconvinced that we need yet another addition to the sprawling world of XML-based formats that are trying to make the semantic web happen."

(This is in response to Simon Willison's posting about wanting to have a way to indicate that two links are related besides just linking to both of them in a weblog post)

Well, I'm happy to report that we don't need another XML format, it already exists: XLink. People already have a name for this idea also, its called a Linkbase