Introduction to RDF

The Resource Description Framework (RDF) is a family of World Wide Web Consortium (W3C) specifications originally designed as a metadata data model.

RDF is a common language:

RDF concepts

RDF identifies resources using Web identifiers called Uniform Resource Identifiers, or URIs.

RDF describes resources using simple statements in the form:

subject > predicate > object

These statements are known as RDF triples.

A set of triples is called an RDF model or graph.

RDF triples

The subject is an URI and denotes the resource.

The predicate is an URI:

The object may be either a literal or an URI. It denotes:

Basically, a triple is the formal representation of a simple sentence with a subject, a verb and an object. Here are some examples of triples where the URIs have been replaced with a human-readable words:

Subject Predicate Object
The sky has the color Blue
John has a brother Jim

In the first triple, the object (blue) is a literal while in the second one, the object (Jim) is an URI. It means it may be used as the subject of another triple.

When put together and displayed as arrows, several triples may compose a complex graph. In the following example of an RDF graph, the resources (URIs) are represented as white shapes while the values (literals) are represented as grey shapes.

RDF graph example

As per the W3C specification, predicates should be URIs. In Componize, predicates are referenced as qualified names instead of URIs because it allows the application to easily relate the predicates to properties from the Alfresco content model.