=head1 NAME

RDF::Lazy::Tutorial - Tutorial to get started with RDF::Lazy

=head1 A short introduction to RDF::Lazy as RDF templating system

=head2 Three kinds of nodes

The basic object in RDF::Lazy is a node (L<RDF::Lazy::Node>). A node represents
an RDF node in an RDF graph. Every nody can be stringified to its value:

    "$x"      Perl syntax
    [% x %]   Template Toolkit syntax
    {$x}      Smarty syntax

There are three kinds of nodes:

=over

=item resource nodes

implemented by L<RDF::Lazy::Resource> and stringified to their URI, for
instance C<http://example.org/foo>.

=item literal nodes

implemented by L<RDF::Lazy::Literal> and stringified to their string value.
instance C<hello world>.

=item blank nodes

implemented by L<RDF::Lazy::Literal> and stringified to C<_:> followed by
their internal blank node identifier, for instance C<_:n0815>.

=back

Nodes have a couple of useful methods. For instance you can check the kind
of a node C<x> with the methods C<is_resource> (or its alias C<is_uri>),
C<is_literal>, and C<is_blank>:

    $x->is_literal                         Perl syntax
    [% x.is_literal %]                     Template Toolkit syntax
    {$x->is_literal} or {$x.is_literal}    Smarty syntax

The method C<str> is automatically called to stringify a node, so C<"$x">
and C<<$x->str>> are equivalent. In HTML templates you can use the method
C<esc> to HTML/XML-escape the stringified node value:

    [% x.esc %]                            Template Toolkit syntax
    {$x->esc} or {$x.esc}                  Smarty syntax

=head2 No nodes without graph

Each node in RDF::Lazy belongs to a particular RDF graph (L<RDF::Lazy>). You
can access a node's graph by its C<graph> method, if needed. Graphs have some
factory methods to create new node objects:

    $g->uri("http://example.org/foo")      A resource node, belonging to $g
    $g->literal("hello world")             A literal node, belonging to $g
    $g->blank("n0815")                     A blank node, belonging to $g

The graph methods C<ttl> and C<ttlpre> are handy o dump the whole graph in 
Turtle syntax. The latter wraps and escapes Turtle for HTML output:

    [% g.ttlpre %]

For instance you can show the number of triples in a node's graph like this:

    <p>The node's graph contains [% x.graph.size %] triples.</p>

=head2 Traversing the graph

One can traverse the RDF graph from any node. For instance, given a
C<foaf:Person> node, one can get another resource linked via C<foaf:knows>: 

    if ( $x->type('foaf:Person') ) {
        $another_person = $x->foaf_knows;
    }

=cut