The XML Files / WebDeveloper.com ®

Getting Deep Into Metadata
Part 2

By Nate Zelnick

The code, boss, the code!

RDF does this with a very simple model for describing the relationship between an object, called a node and some piece of information about it, called a property. The property is given context by a node subset called a PropertyType

An object is referenced by its location, described by its Uniform Resource Identifier (URI). URLs are one type of URIs and is described by its properties. So, the authorship of an article called "RDF Emerges in Metadata Explosion" in the online newspaper called The Foo York Times, written by Lance Foobar could be described like this:

[http://www.fooyorktimes.com/RDF.html] --->Author--->"Lance Foobar"

If we add another property and PropertyType of the URI above so that it reads like this:

[http://www.fooyorktimes.com/RDF.html] --->Title--->"RDF Emerges in Metadata Explosion" |--->Author-->"Lance Foobar"

PropertyTypes are based on specific named elements that are defined in schemas and will require the Namespace specification that is also being worked on by the W3C. Namespaces are needed to avoid having two PropertyTypes with the same name, but different semantics.

As it stands now, RDF will be expressed in XML in something like the following:

<?xml:namespace name="http://www.fooyorktimes.com/WhoWeAre.html" as="FYT"?> <?xml:namespace name="http://www.w3.org/TR/WD-rdf-syntax#" as="RDF"?> <RDF:RDF> <RDF:Description FYT:HREF="http://www.fooyorktimes.com/RDF.html"> <FYT:writer>Lance Foobar </RDF:Description> </RDF:RDF>

This is confusing, I know, but most likely RDF will not be written or consumed by hand. It will be a way for applications to automatically parse XML data and also have some smarts about how to organize the structured content.

Next week: some XML examples you can use today.