RDF/XML, the in place XML syntax for RDF, carries with it certain restrictions imposed by the fact that it is written in XML. Furthermore it uses XML Namespaces that prevent it encoding all RDF graphs, for instance some predicate URI. Turtle is not restricted as such mainly since Turtle is non-XML and is designed with RDF graphs in mind. Turtle being a subset and offshoot of Notation 3 is largely compatible with N3 and is generally useable by systems which support N3. All RDF written in Turtle should be useable inside the query language part of SPARQL Protocol and RDF Query Langage.

Turtle allows for writing down an RDF graph in a compact text form. It consists of a sequence of directives, triple generating statements or blank lines. Simple triples, as defined earlier, are a sequence of terms (subject, predicate, object) separated in Turtle by whitespace and terminated by periods after each triple.

Before delving further we must define a few more terms.

Any expression in RDF is a collection of triples, each consisting of a subject, predicate and object. A set of such triples is called a graph, and can be represented as below.

As mentioned earlier, and depicted above, the triple consists of a subject and an object and how they are related, a predicate indicated by the directioned arrow above. The nodes of the triple are the subject and the object. In all instances the arrow points from the subject to the object.

An RDF triple contains three components:

• The subject, which is an RDF URI reference or a blank node
• The predicate, which is an RDF URI reference
• The object, which is an RDF URI reference, a literal or a blank node.

The predicate is also sometimes termed the 'property' of the triple.

URI

A Uniform Resource Identifer is, as the name says, something used to identify or name resources. Technically it is a compact string of characters meant to be used for identifying and or naming a resource. Resources such as a webpage, a text, a video clip, a program and the list goes on. Typically the URI describres three things: the mechanism for the resource, the computer the resource is hosted on, and the specifc name of the resource (a file name) on the host computer.

The most common type of URI is the URL.

Literal

A literal is a way to identify values such as numbers and dates by means of a lexical representation. In all cases a literal may be replaced by a URI, but literals are more convenient and intuitive to use.

Blank Node

A blank node is a node that is not a URI reference nor a literal but instead is a unique node that can be used in one or more RDF statements, but has no intrinsic name. The blank nodes in an RDF are drawn from an infinite set.