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.\" ========================================================================
.\"
.IX Title "RDF::Lazy::Tutorial 3pm"
.TH RDF::Lazy::Tutorial 3pm "2019-02-20" "perl v5.28.1" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
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.nh
.SH "NAME"
RDF::Lazy::Tutorial \- Tutorial to get started with RDF::Lazy
.SH "A short introduction to RDF::Lazy as RDF templating system"
.IX Header "A short introduction to RDF::Lazy as RDF templating system"
.SS "Three kinds of nodes"
.IX Subsection "Three kinds of nodes"
The basic object in RDF::Lazy is a node (RDF::Lazy::Node). A node represents
an \s-1RDF\s0 node in an \s-1RDF\s0 graph. Every nody can be stringified to its value:
.PP
.Vb 3
\&    "$x"      Perl syntax
\&    [% x %]   Template Toolkit syntax
\&    {$x}      Smarty syntax
.Ve
.PP
There are three kinds of nodes:
.IP "resource nodes" 4
.IX Item "resource nodes"
implemented by RDF::Lazy::Resource and stringified to their \s-1URI,\s0 for
instance \f(CW\*(C`http://example.org/foo\*(C'\fR.
.IP "literal nodes" 4
.IX Item "literal nodes"
implemented by RDF::Lazy::Literal and stringified to their string value.
instance \f(CW\*(C`hello world\*(C'\fR.
.IP "blank nodes" 4
.IX Item "blank nodes"
implemented by RDF::Lazy::Literal and stringified to \f(CW\*(C`_:\*(C'\fR followed by
their internal blank node identifier, for instance \f(CW\*(C`_:n0815\*(C'\fR.
.PP
Nodes have a couple of useful methods. For instance you can check the kind
of a node \f(CW\*(C`x\*(C'\fR with the methods \f(CW\*(C`is_resource\*(C'\fR (or its alias \f(CW\*(C`is_uri\*(C'\fR),
\&\f(CW\*(C`is_literal\*(C'\fR, and \f(CW\*(C`is_blank\*(C'\fR:
.PP
.Vb 3
\&    $x\->is_literal                         Perl syntax
\&    [% x.is_literal %]                     Template Toolkit syntax
\&    {$x\->is_literal} or {$x.is_literal}    Smarty syntax
.Ve
.PP
The method \f(CW\*(C`str\*(C'\fR is automatically called to stringify a node, so \f(CW"$x"\fR
and \f(CW\*(C`<$x\-\*(C'\fRstr>> are equivalent. In \s-1HTML\s0 templates you can use the method
\&\f(CW\*(C`esc\*(C'\fR to HTML/XML\-escape the stringified node value:
.PP
.Vb 2
\&    [% x.esc %]                            Template Toolkit syntax
\&    {$x\->esc} or {$x.esc}                  Smarty syntax
.Ve
.SS "No nodes without graph"
.IX Subsection "No nodes without graph"
Each node in RDF::Lazy belongs to a particular \s-1RDF\s0 graph (RDF::Lazy). You
can access a node's graph by its \f(CW\*(C`graph\*(C'\fR method, if needed. Graphs have some
factory methods to create new node objects:
.PP
.Vb 3
\&    $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
.Ve
.PP
The graph methods \f(CW\*(C`ttl\*(C'\fR and \f(CW\*(C`ttlpre\*(C'\fR are handy o dump the whole graph in 
Turtle syntax. The latter wraps and escapes Turtle for \s-1HTML\s0 output:
.PP
.Vb 1
\&    [% g.ttlpre %]
.Ve
.PP
For instance you can show the number of triples in a node's graph like this:
.PP
.Vb 1
\&    <p>The node\*(Aqs graph contains [% x.graph.size %] triples.</p>
.Ve
.SS "Traversing the graph"
.IX Subsection "Traversing the graph"
One can traverse the \s-1RDF\s0 graph from any node. For instance, given a
\&\f(CW\*(C`foaf:Person\*(C'\fR node, one can get another resource linked via \f(CW\*(C`foaf:knows\*(C'\fR:
.PP
.Vb 3
\&    if ( $x\->type(\*(Aqfoaf:Person\*(Aq) ) {
\&        $another_person = $x\->foaf_knows;
\&    }
.Ve