NAME
    RDF::RDFa::Parser - flexible RDFa parser

SYNOPSIS
     use RDF::RDFa::Parser;
 
     ### Create an object...
     $p = RDF::RDFa::Parser->new_from_url($url);
     # or: $p = RDF::RDFa::Parser->new($markup, $base_url);
 
     ### Get an RDF::Trine::Model containing the document's data...
     $data = $p->graph;
 
     ### Get Open Graph Protocol data...
     $title = $p->opengraph('title');

VERSION
    1.091

DESCRIPTION
  Constructors
    "$p = RDF::RDFa::Parser->new($markup, $base, [$config], [$storage])"
        This method creates a new RDF::RDFa::Parser object and returns it.

        The $markup variable may contain an XHTML/XML string, or a
        XML::LibXML::Document. If a string, the document is parsed using
        XML::LibXML::Parser or HTML::HTML5::Parser, depending on the
        configuration in $config. XML well-formedness errors will cause the
        function to die.

        $base is a URL used to resolve relative links found in the document.

        $config optionally holds an RDF::RDFa::Parser::Config object which
        determines the set of rules used to parse the RDFa. It defaults to
        XHTML+RDFa 1.1.

        Advanced usage note: $storage optionally holds an RDF::Trine::Store
        object. If undef, then a new temporary store is created.

    "$p = RDF::RDFa::Parser->new_from_url($url, [$config], [$storage])"
        $url is a URL to fetch and parse.

        $config optionally holds an RDF::RDFa::Parser::Config object which
        determines the set of rules used to parse the RDFa. The default is
        to determine the configuration by looking at the HTTP response
        Content-Type header; it's probably sensible to keep the default.

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

        This function can also be called as "new_from_uri". Same thing.

    "$p = RDF::RDFa::Parser->new_from_response($response, [$config],
    [$storage])"
        $response is an "HTTP::Response" object.

        Otherwise the same as "new_from_url".

  Public Methods
    "$p->graph"
        This will return an RDF::Trine::Model containing all the RDFa data
        found on the page.

        Advanced usage note: If passed a graph URI as a parameter, will
        return a single named graph from within the page. This feature is
        only useful if you're using named graphs.

    "$p->graphs"
        Advanced usage only.

        Will return a hashref of all named graphs, where the graph name is a
        key and the value is a RDF::Trine::Model tied to a temporary
        storage.

        This method is only useful if you're using named graphs.

    "$p->opengraph([$property])"
        If $property is provided, will return the value or list of values
        (if called in list context) for that Open Graph Protocol property.
        (In pure RDF terms, it returns the non-bnode objects of triples
        where the subject is the document base URI; and the predicate is
        $property, with non-URI $property strings taken as having the
        implicit prefix 'http://ogp.me/ns#'. There is no distinction between
        literal and non-literal values.)

        If $property is omitted, returns a list of possible properties.

        Example:

          foreach my $property (sort $p->opengraph)
          {
            print "$property :\n";
            foreach my $val (sort $p->opengraph($property))
            {
              print "  * $val\n";
            }
          }

        See also: <http://opengraphprotocol.org/>.

    "$p->dom"
        Returns the parsed XML::LibXML::Document.

    "$p->uri( [$other_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->errors"
        Returns a list of errors and warnings that occurred during parsing.

    "$p->consume"
        Advanced usage only.

        The document is parsed for RDFa. As of RDF::RDFa::Parser 1.09x, this
        is called automatically when needed; you probably don't need to
        touch it unless you're doing interesting things with callbacks.

    "$p->set_callbacks(\%callbacks)"
        Advanced usage only.

        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 ,
            'onprefix'           => \&some_function ,
            });

        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. If
        used, "set_callbacks" must be called *before* "consume".
        "set_callbacks" returns a reference to the parser object itself.

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 "RDF::RDFa::Parser" object

    *   A reference to the "XML::LibXML::Element" being parsed

    *   Subject URI or bnode (string)

    *   Predicate URI (string)

    *   Object URI or bnode (string)

    *   Graph URI or bnode (string or undef)

    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 "RDF::RDFa::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)

    *   Graph URI or bnode (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 "RDF::RDFa::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.

  onprefix
    This is called when a new CURIE prefix is discovered. The parameters
    passed to the callback function are:

    *   A reference to the "RDF::RDFa::Parser" object

    *   A reference to the "XML::LibXML::Element" being parsed

    *   The prefix (string, e.g. "foaf")

    *   The expanded URI (string, e.g. "http://xmlns.com/foaf/0.1/")

    The return value of this callback is currently ignored, but you should
    return 0 in case future versions of this module assign significance to
    the return value.

  ontoken
    This is called when a CURIE has been expanded. The parameters are:

    *   A reference to the "RDF::RDFa::Parser" object

    *   A reference to the "XML::LibXML::Element" being parsed

    *   The CURIE or token as a string (e.g. "foaf:name" or "Stylesheet")

    *   The fully expanded URI

    The callback function must return a fully expanded URI, or if it wants
    the CURIE to be ignored, undef.

  onerror
    This is called when an error occurs:

    *   A reference to the "RDF::RDFa::Parser" object

    *   The error level (RDF::RDFa::Parser::ERR_ERROR or
        RDF::RDFa::Parser::ERR_WARNING)

    *   An error code

    *   An error message

    *   A hash of other information

    The return value of this callback is currently ignored, but you should
    return 0 in case future versions of this module assign significance to
    the return value.

    If you do not define an onerror callback, then errors will be output via
    STDERR and warnings will be silent. Either way, you can retrieve errors
    after parsing using the "errors" method.

FEATURES
    Most features are configurable using RDF::RDFa::Parser::Config.

  RDFa Versions
    RDF::RDFa::Parser supports RDFa versions 1.0 and 1.1.

    1.1 is currently a moving target; support is experimental.

    1.1 is the default, but this can be configured using
    RDF::RDFa::Parser::Config.

  Host Languages
    RDF::RDFa::Parser supports various different RDFa host languages:

    *   XHTML

        As per the XHTML+RDFa 1.0 and XHTML+RDFa 1.1 specifications.

    *   HTML 4

        Uses an HTML5 (sic) parser; uses @lang instead of @xml:lang; keeps
        prefixes and terms case-insensitive; recognises the @rel relations
        defined in the HTML 4 specification. Otherwise the same as XHTML.

    *   HTML5

        Uses an HTML5 parser; uses @lang as well as @xml:lang; keeps
        prefixes and terms case-insensitive; recognises the @rel relations
        defined in the HTML5 draft specification. Otherwise the same as
        XHTML.

    *   XML

        This is implemented as per the RDFa Core 1.1 specification. There is
        also support for "RDFa Core 1.0", for which no specification exists,
        but has been reverse-engineered by applying the differences between
        XHTML+RDFa 1.1 and RDFa Core 1.1 to the XHTML+RDFa 1.0
        specification.

        Embedded chunks of RDF/XML within XML are supported.

    *   SVG

        For now, a synonym for XML.

    *   Atom

        The <feed> and <entry> elements are treated specially, setting a new
        subject; IANA-registered rel keywords are recognised.

        By passing "atom_parser=>1" as a Config option, you can also handle
        Atom's native semantics. (Uses XML::Atom::OWL. If this module is not
        installed, this option is silently ignored.)

        Otherwise, the same as XML.

    *   DataRSS

        Support for the <?profile?> processing instruction; defines some
        default prefixes. Otherwise, the same as Atom.

    *   OpenDocument XML

        That is, XML content formatted along the lines of 'content.xml' in
        OpenDocument files.

        Supports OpenDocument bookmarked ranges used as typed or plain
        object literals (though not XML literals); expects RDFa attributes
        in the XHTML namespace instead of in no namespace. Otherwise, the
        same as XML.

    *   OpenDocument

        That is, a ZIP file containing OpenDocument XML files.
        RDF::RDFa::Parser will do all the unzipping and combining for you,
        so you don't have to. The unregistered "jar:" URI scheme is used to
        refer to files within the ZIP.

  Embedded RDF/XML
    Though a rarely used feature, XHTML allows other XML markup languages to
    be directly embedded into it. In particular, chunks of RDF/XML can be
    included in XHTML. While this is not common in XHTML, it's seen quite
    often in SVG and other XML markup languages.

    When RDF::RDFa::Parser encounters a chunk of RDF/XML in a document it's
    parsing (i.e. an element called 'RDF' with namespace
    'http://www.w3.org/1999/02/22-rdf-syntax-ns#'), there are three
    different courses of action it can take:

    0. Continue straight through it.
        This is the behaviour that XHTML+RDFa seems to suggest is the right
        option. It should mostly not do any harm: triples encoded in RDF/XML
        will be generally ignored (though the chunk itself could
        theoretically end up as part of an XML literal). It will waste a bit
        of time though.

    1. Parse the RDF/XML.
        The parser will parse the RDF/XML properly. If named graphs are
        enabled, any triples will be added to a separate graph. This is the
        behaviour that SVG Tiny 1.2 seems to suggest is the correct thing to
        do.

    2. Skip the chunk.
        This will skip over the RDF element entirely, and thus save you a
        bit of time.

    You can decide which path to take by setting the 'embedded_rdfxml'
    Config option. For HTML and XHTML, you probably want to set
    embedded_rdfxml to '0' (the default) or '2' (a little faster). For other
    XML markup languages (e.g. SVG or Atom), then you probably want to set
    it to '1'.

    (There's also an option '3' which controls how embedded RDF/XML
    interacts with named graphs, but this is only really intended for
    internal use, parsing OpenDocument.)

  Named Graphs
    The parser has support for named graphs within a single RDFa document.
    To switch this on, use the 'graph' Config option.

    See also <http://buzzword.org.uk/2009/rdfa4/spec>.

    The name of the attribute which indicates graph URIs is by default
    'graph', but can be changed using the 'graph_attr' Config option. This
    option accepts Clark Notation to specify a namespaced attribute. By
    default, the attribute value is interpreted as a fragment identifier
    (like the 'id' attribute), but if you set the 'graph_type' Config option
    to 'about', it will be treated as a URI or safe CURIE (like the 'about'
    attribute).

    The 'graph_default' Config option allows you to set the default graph
    URI/bnode identifier.

    Once you're using named graphs, the "graphs" method becomes useful: it
    returns a hashref of { graph_uri => trine_model } pairs. The optional
    parameter to the "graph" method also becomes useful.

    OpenDocument (ZIP) host language support makes internal use of named
    graphs, so if you're parsing OpenDocument, tinker with the Config
    options at your own risk!

  Auto Config
    RDF::RDFa::Parser has a lot of different Config options to play with.
    Sometimes it might be useful to allow the page being parsed to control
    some of these options. If you switch on the 'auto_config' Config option,
    pages can do this.

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

      <meta name="http://search.cpan.org/dist/RDF-RDFa-Parser/#auto_config"
         content="xhtml_lang=1&amp;keyword_bundles=rdfa+html5+html4+html32" />

    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/RDF-RDFa-Parser/#auto_config"
         content="xhtml_lang=1;keyword_bundles=rdfa+html5+html4+html32" />

    It's possible to use auto config outside XHTML (e.g. in Atom or SVG)
    using namespaces:

      <xhtml:meta xmlns:xhtml="http://www.w3.org/1999/xhtml"
         name="http://search.cpan.org/dist/RDF-RDFa-Parser/#auto_config"
         content="keyword_bundles=iana+rdfa;xml_base=2;atom_elements=1" />

    Any Config option may be given using auto config, except 'use_rtnlx',
    'dom_parser', and of course 'auto_config' itself.

BUGS
    RDF::RDFa::Parser 0.21 passed all approved tests in the XHTML+RDFa test
    suite at the time of its release.

    RDF::RDFa::Parser 0.22 (used in conjunction with HTML::HTML5::Parser
    0.01 and HTML::HTML5::Sanity 0.01) additionally passes all approved
    tests in the HTML4+RDFa and HTML5+RDFa test suites at the time of its
    release; except test cases 0113 and 0121, which the author of this
    module believes mandate incorrect HTML parsing.

    Please report any bugs to <http://rt.cpan.org/>.

    Common gotchas:

    *       Are you using the XML catalogue?

            RDF::RDFa::Parser maintains a locally cached version of the
            XHTML+RDFa DTD. This will normally be within your Perl module
            directory, in a subdirectory named
            "auto/share/dist/RDF-RDFa-Parser/catalogue/". If this is
            missing, the parser should still work, but will be very slow.

SEE ALSO
    RDF::RDFa::Parser::Config, RDF::RDFa::Parser::Profile.

    XML::LibXML, RDF::Trine, HTML::HTML5::Parser, HTML::HTML5::Sanity,
    XML::Atom::OWL.

    <http://www.perlrdf.org/>.

AUTHOR
    Toby Inkster <tobyink@cpan.org>.

ACKNOWLEDGEMENTS
    Kjetil Kjernsmo <kjetilk@cpan.org> wrote much of the stuff for building
    RDF::Trine models. Neubert Joachim taught me to use XML catalogues,
    which massively speeds up parsing of XHTML files that have DTDs.

COPYRIGHT
    Copyright 2008-2010 Toby Inkster

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

