How Does RDF Work?
RDF works by expressing statements about resources, which can be anything. A resource does not even have to exist. One can describe whatever one wants to in RDF by putting together an RDF statement about that resource. In theory, a single RDF statement resembles a simple English sentence. For example, a typical simple English sentence is structured in the following way: Subject-Verb-Object. A typical RDF statement is made up of the three following components: Subject-Predicate-Object. These Subject-Predicate-Object triples are often referred to as just that: RDF triples.
The Subject is always a web resource. In RDF, a resource is represented by a URI. Unlike a URL, a URI is not used to locate resources, only to identify them (hence the I for Identifier instead of the L for Locator). A Predicate describes the Subject (an example of this is upcoming). Finally, the Object can be either another resource or a simple constant, possibly representing a number, string or date.
The expression "Alex is writing an article" would look something like this in an RDF triple:
Alex isWriting Article
While the triples concept is intuitive because of its close relation to English, RDF syntax is a bit cryptic because it is meant for machine readability. In recent years, more human-readable RDF syntaxes have been introduced, but simple statements can still produce bulky and cryptic XML. For example, here is a snippet of real RDF that represents the simple expression "Alex is writing an article":
Ultimately, the size and complexity of the XML is not a huge concern because the cryptic syntax is meant for computers. Also because it is meant for machines, one can put together large collections of statements. A large and/or comprehensive collection of statements about a subject (such as wine for example) is a body of data that in the philosophy of knowledge is known as an ontology. Hence, in Semantic Web, one can make ontologies in RDF and infinitely share them.