The Class of a Node is its rdf:type Property

When you read RDF- say, a FOAF file, the RdfXmlSyntax code looks like...

<foaf:Person>
  <foaf:name>Your Name Here</foaf:name>
  <foaf:nick>YourNick</foaf:nick>
  ...
</foaf:Person>

The outermost foaf:Person is called the class of the node produced.

That is, there is a node produced, and it's "class" is foaf:Person.

But we know that RDF is all about graphs of nodes, and there are only subject, predicate, and object (SubjectPredicateObject.)

subjects: (nodes)
predicates: (paths from subjects to objects)
objects: (nodes, or literals)

Where then is the notion of a "Class?"

The answer is that it is actually a property (aka "predicate.")

That is, when you say:

<foaf:Person>
  ...
</foaf:Person>

...then you are actually saying: "There is a node, and an RdfStatement attached to this node, automatically."

That statement is:

(node) rdf:type foaf:Person

Discussion

CharlesNepote asks a good question on his page:

Is...

<Prohibition rdf:about="http://web.resource.org/cc/CommercialUse">
  <dc:title>Commercial Use</dc:title>
  <dc:description>rights may be exercised for commercial purposes</dc:description>
</Prohibition>

...the same as...

<cc:CommercialUse>
  <rdf:type rdf:resource="cc:Prohibition">
  <dc:title>Commercial Use</dc:title>
  <dc:description>rights may be exercised for commercial purposes</dc:description>
</cc:CommercialUse>

...?

I would think not, because cc:[[CommercialUse]] would seem to be itself interpreted as a Class here.

I have additional questions:

Is it possible for a node to belong to two classes?
How do you make a class-less node? Or is that even possible?

-- LionKimbro DateTime(2004-06-14T02:22:08)

As far as RDF is concerned, rdf:type is no different from any other property, so a given resource can have any number of values for rdf:type. The RdfXmlSyntax has some shortcuts for declaring rdf:type, which is probably what is confusing people.

This:

  <rdf:Description rdf:about='http://example.com/thing'>
    <rdf:type rdf:resource='http://vocab.example.com/Thing'/>
    <dc:title>Example thing</dc:title>
  </rdf:Description>

can be abbreviated as:

  <rdf:Description rdf:about='http://example.com/thing' rdf:type='http://vocab.example.com/Thing'>
    <dc:title>Example thing</dc:title>
  </rdf:Description>

or:

  <ex:Thing rdf:about='http://example.com/thing' xmlns:ex='http://vocab.example.com/'>
    <dc:title>Example thing</dc:title>
  </ex:Thing>

All three will produce the same graph:

   <http://example.com/thing>
   <http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
   <http://vocab.example.com/Thing>.

   <http://example.com/thing>
   <http://purl.org/dc/elements/1.1/title>
   "Example thing".

Using the RdfXmlSyntax, one can use rdf:Description to describe a resource without specifying its type. To give a resource multiple types, you can declare the rdf:type properties explicitly or use use the abbreviated form multiple times:

  <Class1 rdf:about='http://example.com/whatever'>
    <rdf:type resource='http://vocab.example.com/Class2'/>
    <rdf:type resource='http://vocab.example.com/Class3'/>
  </Class1>

or:

  <Class1 rdf:about='http://example.com/whatever'/>
  <Class2 rdf:about='http://example.com/whatever'/>
  <Class3 rdf:about='http://example.com/whatever'/>

-- David Menendez DateTime