For years, I thought that XML was the king and RDF was its knight. Well, I got it all wrong: it's the other way around, it's just that it's very hard to realize it.
People in all sort of communities realize how important semi-structured data is and how much it will be in the future. These people tend to think that XML will solve the problem for them and once we have a serious XML query language, we'll be set forever.
Well, wrong. Relations are tables, XML documents are trees, and, guess what, RDF models are graphs. Yep, you got it, RDF candescribe both.
The more I discover RDF and RDF query languages, the more it seems to me that it was all about that stupid RDF/XML syntax that prevented people from getting what RDF really was. RDF is a model for describing labelled directed graphs. That's it. You can add typing (RDFSchema) or inference (OWL), but the real deal is that you now have a way to describe graphs.
Many people tend to think at RDF as a uselessly complex way to write markup more formally. Some people tend to think that if XML is data, RDF is metadata. Wrong and wrong. An RDF model is a graph. Period. And since all trees and tables are graphs, you can have an RDF representation of any kind of data you want.