Last time we looked at the general concept of what meta data is and why it is a key concept for understanding one of the ways that XML is going to be used for Web documents.
Now it's time to get down deep and dirty into one of the ways that XML is being extended so that structured data can be passed around the Web from machine to machine in a completely automatic fashion. That technology, called the Resource Description Framework (or RDF) has been a draft specification at the World Wide Web Consortium since February.
Ironically, RDF's origins are as a competitor to one of the first XML vocabularies publicly available: Microsoft's Channel Definition (CDF), which was used as the basis of a demo application a few columns ago. What CDF is to Microsoft's limping Active Channel effort, RDF is to Netscape's Aurora technology. RDF will also be the basis for Navigator 5.0's clone of the channel bars for bookmarks, history, etc. that Microsoft introduced in Internet Explorer 4.0.
Netscape has been muddled on the relationship between XML and RDF in the past--going as far as saying "When you think XML, think RDF" on more than one occasion. That changed fast when it became clear that XML was emerging as the preferred way to express structure in documents generically. RDF will now be expressed in XML. To get a sense of what Netscape wants to do with RDF, you can take a look at this demo, written in a pre-XML version of the technology. It will only work with Navigator 4.0 and later.
RDF is a way to say something about something. While this seems straightforward, it's actually pretty nuanced when you're in the context of the Web because you can have little assurance of anything on the Web ahead of time. To describe the relationship of one thing to another thing, you need to have a very clear way for the unknown party that will be trying to figure out that relationship to understand what you're trying to say.
and find truth, justice, and a clue or two.
