Metadata and the Semantic Web - Web Standards: Mastering HTML5, CSS3, and XML - page 258

Listing 7-54. The N3 Equivalent of the Previous Example

@prefix : <http://www.example.org/~joe/contact.rdf#> .
@prefix foaf: < http://xmlns.com/foaf/0.1/ > .
@prefix rdf: < http://www.w3.org/1999/02/22-rdf-syntax-ns# > .
:joesmith a foaf:Person ;
foaf:givenname "Joe" ;
foaf:family_name "Smith" ;
foaf:homepage <http://www.example.org/~joe/> ;
foaf:mbox <mailto:[e-mail]>.

The RDF namespace is http://www.w3.org/1999/02/22-rdf-syntax-ns# , which is conventionally associated
with the namespace prefix rdf: .
The Unicode strings in URI references of RDF graphs cannot contain control characters ( #x00 - #x1F , #x7F - #x9F ).
These URIs should be absolute URIs with optional fragment identifiers.
RDF literals are used to identify values such as numbers and dates. RDF literals are Unicode strings containing one or
two named components. They should be written in UTF-8 normalized in Normalization Form C (Canonical Decomposition
followed by Canonical Composition [122]). RDF literals can be either plain or typed. Plain literals are strings combined with
an optional language tag (normalized to lowercase). They correspond to plain text in a natural language. Typed literals are
strings combined with a datatype URI for applying the lexical-to-value mapping to the literal string.
The Formal Grammar of the Resource Description Framework was introduced in 1999 [123]. RDF has the
following vocabulary:

rdf:Alt , rdf:Bag , rdf:Seq •

Containers of alternatives, unordered containers, and ordered containers ( rdfs:Container is
a superclass of the three)

rdf:List •

The class of RDF lists

rdf:nil
An empty list (an instance of rdf:List )

•

rdf:Property •

The class of properties

rdf:Statement , rdf:subject , rdf:predicate , rdf:object •

Reification

rdf:type

•

A predicate that identifies the class that the resource is an instance of

rdf:XMLLiteral •

The class of typed literals

This vocabulary is also used as the basis for the extensible knowledge representation language, RDF Schema
(see the section “RDF Schema”).
There is a query language called SPARQL (pronounced “Sparkle”) that can be used to retrieve and manipulate
information stored in RDF or in any format that can be retrieved as RDF [124]. The output can be a results set or an RDF
graph. It is also possible to update RDF graphs through a protocol known as the SPARQL 1.1 Uniform HTTP Protocol [125].