Resource Description Framework (RDF) is one of the most exciting new standards to emerge from the World Wide Web Consortium (W3C)the people who gave us XML. It's also the most widely misunderstood topic since XML itself. That's because RDF is all about metadata, and metadata is a slippery topic. In my book XML and SQL: Developing Web Applications (publication details below), I describe an approach (called partial decomposition) to extracting metadata from XML documents and storing this metadata in SQL databases.
I remember getting feedback from a technical reviewer saying that I had misunderstood the term metadata. This reviewer felt that metadata represented things like field lengths (such as 160 bytes) and datatypes (string, integer, etc.). The reviewer was rightin the context familiar to him or herbut didn't understand that metadata can have another context: a content-centric context.
If you're familiar with XML, you know that XML isn't actually a markup language in and of itself. XML is a framework for creating markupit's a set of markup "rules to live by." RDF is the same kind of animal as XML. It isn't a metadata standardit's a way to build metadata standards and a standard way to represent metadata in XML form. RDF stands for Resource Description Framework, and it's just that: a framework that can be used in many different contexts to achieve many different goals.
RDF goes one step beyond a standard representation of metadata. RDF is self-describing metadata. Used properly, RDF metadata can describe itself to whomever happens to be listening.