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HTML-HTML5-Microdata-Parser-0.100
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/ HTML::HTML5::Microdata::Parser

NAME

HTML::HTML5::Microdata::Parser - fairly experimental parser for HTML 'microdata'

SYNOPSIS

use HTML::HTML5::Microdata::Parser;

my $parser = HTML::HTML5::Microdata::Parser->new($html, $baseURI);
my $graph  = $parser->graph;

DESCRIPTION

This package aims to have a roughly compatible API to RDF::RDFa::Parser.

Microdata is an experimental metadata format, not in wide use. Use this module at your own risk.

$p = HTML::HTML5::Microdata::Parser->new($html, $baseuri, \%options, $storage)

This method creates a new HTML::HTML5::Microdata::Parser object and returns it.

The $xhtml variable may contain an XHTML/XML string, or a XML::LibXML::Document. If a string, the document is parsed using HTML::HTML5::Parser and HTML::HTML5::Sanity, which may throw an exception. HTML::HTML5::Microdata::Parser does not catch the exception.

The base URI is used to resolve relative URIs found in the document.

Options [default in brackets]:

* alt_stylesheet  - Magic rel="alternate stylesheet". [1]
* auto_config     - See section "Auto Config" [0]
* mhe_lang        - Process <meta http-equiv=Content-Language>.
                    [1]
* prefix_empty    - URI prefix for itemprops of untyped items.
                    [undef]
* strategy        - URI generation strategy for itemprops of
                    typed items. [HTML::HTML5::Microdata::
                    Strategy::Heuristic]
* tdb_service     - thing-described-by.org when possible. [0] 
* xhtml_base      - Process <base href> element. [1]
* xhtml_lang      - Process @lang. [1]
* xhtml_meta      - Process <meta>. [0]
* xhtml_cite      - Process @cite. [0]
* xhtml_rel       - Process @rel. [0]
* xhtml_time      - Process <time> element more nicely. [0]
* xhtml_title     - Process <title> element. [0]
* xml_lang        - Process @xml:lang. [1]

$storage is an RDF::Trine::Storage object. If undef, then a new temporary store is created.

$p->xhtml

Returns the HTML source of the document being parsed.

$p->uri

Returns the base URI of the document being parsed. This will usually be the same as the base URI provided to the constructor, but may differ if the document contains a <base> HTML element.

Optionally it may be passed a parameter - an absolute or relative URI - in which case it returns the same URI which it was passed as a parameter, but as an absolute URI, resolved relative to the document's base URI.

This seems like two unrelated functions, but if you consider the consequence of passing a relative URI consisting of a zero-length string, it in fact makes sense.

$p->dom

Returns the parsed XML::LibXML::Document.

$p->set_callbacks(\%callbacks)

Set callback functions for the parser to call on certain events. These are only necessary if you want to do something especially unusual.

$p->set_callbacks({
  'pretriple_resource' => sub { ... } ,
  'pretriple_literal'  => sub { ... } ,
  'ontriple'           => undef ,
  });

Either of the two pretriple callbacks can be set to the string 'print' instead of a coderef. This enables built-in callbacks for printing Turtle to STDOUT.

For details of the callback functions, see the section CALLBACKS. set_callbacks must be used before consume. set_callbacks itself returns a reference to the parser object itself.

$p->consume

The document is parsed for Microdata. Nothing of interest is returned by this function, but the triples extracted from the document are passed to the callbacks as each one is found.

The graph method automatically calls consume, so normally you don't need to call it manually. If you're using callback functions, it may be useful though.

$p->consume_microdata_item($element)

You almost certainly do not want to use this method.

It will consume a single Microdata item, assuming that $element is an element that does or should have the @itemscope attribute set. Returns the URI or blank node identifier for the item.

This method is exposed mostly for the benefit of HTML::HTML5::Microdata::ToRDFa.

$p->graph()

This method will return an RDF::Trine::Model object with all statements of the full graph.

$p->graphs()

Provided for RDF::RDFa::Parser compatibility.

CALLBACKS

Several callback functions are provided. These may be set using the set_callbacks function, which taskes a hashref of keys pointing to coderefs. The keys are named for the event to fire the callback on.

pretriple_resource

This is called when a triple has been found, but before preparing the triple for adding to the model. It is only called for triples with a non-literal object value.

The parameters passed to the callback function are:

  • A reference to the HTML::HTML5::Microdata::Parser object

  • A reference to the XML::LibXML::Element being parsed

  • Subject URI or bnode (string)

  • Predicate URI (string)

  • Object URI or bnode (string)

The callback should return 1 to tell the parser to skip this triple (not add it to the graph); return 0 otherwise.

pretriple_literal

This is the equivalent of pretriple_resource, but is only called for triples with a literal object value.

The parameters passed to the callback function are:

  • A reference to the HTML::HTML5::Microdata::Parser object

  • A reference to the XML::LibXML::Element being parsed

  • Subject URI or bnode (string)

  • Predicate URI (string)

  • Object literal (string)

  • Datatype URI (string or undef)

  • Language (string or undef)

Beware: sometimes both a datatype and a language will be passed. This goes beyond the normal RDF data model.)

The callback should return 1 to tell the parser to skip this triple (not add it to the graph); return 0 otherwise.

ontriple

This is called once a triple is ready to be added to the graph. (After the pretriple callbacks.) The parameters passed to the callback function are:

  • A reference to the HTML::HTML5::Microdata::Parser object

  • A reference to the XML::LibXML::Element being parsed

  • An RDF::Trine::Statement object.

The callback should return 1 to tell the parser to skip this triple (not add it to the graph); return 0 otherwise. The callback may modify the RDF::Trine::Statement object.

ITEMPROP URI GENERATION STRATEGY

The itemprop attribute does not need to be a full URI.

<div itemscope itemtype="http://example.com/Person">
  <span itemprop="phoneNumber">01234 567 890</span>
</div>

The strategy option passed to the constructor tells the parser how to convert phoneNumber in the above example into a URI. This can be a callback function, or an object or class that provides a generate_uri method.

Three strategies are bundled with this distribution:

  • HTML::HTML5::Microdata::Strategy::Basic - don't attempt to convert to a URI

  • HTML::HTML5::Microdata::Strategy::Heuristic - smart strategy, the default

  • HTML::HTML5::Microdata::Strategy::Microdata0 - official strategy of early Microdata drafts

AUTO CONFIG

HTML::HTML5::Microdata::Parser has a lot of different options that can be switched on and off. Sometimes it might be useful to allow the page being parsed to control some of the options. If you switch on the 'auto_config' option, pages can do this.

A page can set options using a specially crafted <meta> tag:

<meta name="http://search.cpan.org/dist/HTML-HTML5-Microdata-Parser/#auto_config"
   content="alt_stylesheet=0&amp;prefix_empty=http://example.net/" />

Note that the content attribute is an application/x-www-form-urlencoded string (which must then be HTML-escaped of course). Semicolons may be used instead of ampersands, as these tend to look nicer:

<meta name="http://search.cpan.org/dist/HTML-HTML5-Microdata-Parser/#auto_config"
   content="alt_stylesheet=0;prefix_empty=http://example.net/" />

Any option allowed in the constructor may be given using auto config, except 'auto_config' itself.

SEE ALSO

XML::LibXML, RDF::Trine, RDF::RDFa::Parser, HTML::HTML5::Parser, HTML::HTML5::Sanity.

http://www.perlrdf.org/.

AUTHOR

Toby Inkster <tobyink@cpan.org>.

COPYRIGHT AND LICENCE

Copyright (C) 2009-2011 by Toby Inkster

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

DISCLAIMER OF WARRANTIES

THIS PACKAGE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.