RDF::RDFa::Parser - flexible RDFa parser
use RDF::RDFa::Parser; $parser = RDF::RDFa::Parser->new(undef, $uri)->consume; $graph = $parser->graph;
1.00_01
This method creates a new RDF::RDFa::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 XML::LibXML::Parser, which will throw an exception if it is not well-formed. RDF::RDFa::Parser does not catch the exception.
The base URI is needed to resolve relative URIs found in the document. If $xhtml is undef, then RDF::RDFa::Parser will fetch $baseuri to obtain the document to be parsed.
Options (mostly booleans) [default in brackets]:
* alt_stylesheet - Magic rel="alternate stylesheet". [0] * atom_elements - Process <feed> and <entry> specially. [0] * atom_parser - Extract Atom 1.0 native semantics. [0] * auto_config - See section "Auto Config" [0] * embedded_rdfxml - Find plain RDF/XML chunks within document. [0] 0=no, 1=handle, 2=skip. * full_uris - Support full URIs in CURIE-only attributes. [0] * graph - Enable support for named graphs. [0] * graph_attr - Attribute to use for named graphs. ['graph'] Use Clark Notation to specify a namespace. * graph_type - Graph attr behaviour ('id' or 'about'). ['id'] * graph_default - Default graph name. ['_:RDFaDefaultGraph'] * keywords - THIS WILL VOID YOUR WARRANTY! * prefix_attr - Support @prefix rather than just @xmlns:*. [0] * prefix_bare - Support CURIEs with no colon+suffix. [0] * prefix_default - URI for default prefix (e.g. rel="foo"). [undef] * prefix_empty - URI for empty prefix (e.g. rel=":foo"). ['http://www.w3.org/1999/xhtml/vocab#'] * prefix_nocase - Ignore case-sensitivity of CURIE prefixes. [0] * safe_anywhere - Allow Safe CURIEs in @rel/@rev/etc. [0] * tdb_service - Use thing-described-by.org to name bnodes. [0] * use_rtnlx - Use RDF::Trine::Node::Literal::XML. [0] 0=no, 1=if available. * xhtml_base - Process <base> element. [1] 0=no, 1=yes, 2=use it for RDF/XML too * xhtml_elements - Process <head> and <body> specially. [1] * xhtml_lang - Support @lang rather than just @xml:lang. [0] * xml_base - Support for 'xml:base' attribute. [0] 0=only RDF/XML; 1=except @href/@src; 2=always. * xml_lang - Support for 'xml:lang' attribute. [1]
The default options attempt to stick to the XHTML+RDFa spec as rigidly as possible.
$storage is an RDF::Trine::Store object. If undef, then a new temporary store is created.
Returns the XHTML source of the document being parsed.
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.
Returns the parsed XML::LibXML::Document.
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. set_callbacks must be used before consume. set_callbacks itself returns a reference to the parser object itself.
set_callbacks
consume
The document is parsed for RDFa. Triples extracted from the document are passed to the callbacks as each one is found; triples are made available in the model returned by the graph method.
graph
This function returns the parser object itself, making it easy to abbreviate several of RDF::RDFa::Parser's functions:
my $iterator = RDF::RDFa::Parser->new($xhtml,$uri) ->consume->graph->as_stream;
Without a graph name, this method will return an RDF::Trine::Model object with all statements of the full graph. As per the RDFa specification, it will always return an unnamed graph containing all the triples of the RDFa document. If the model contains multiple graphs, all triples will be returned unless a graph name is specified.
It will also take an optional graph URI as argument, and return an RDF::Trine::Model tied to a temporary storage with all triples in that graph.
It makes sense to call consume before calling graph. Otherwise you'll just get an empty graph.
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.
It makes sense to call consume before calling graphs. Otherwise you'll just get an empty hashref.
graphs
Without any options, gets an empty structure for keywords. Passing additional strings adds certain bundles of predefined keywords to the structure.
my $keyword_structure = RDF::RDFa::Parser::keywords( 'xhtml', 'xfn', 'grddl');
A keyword structure may be provided as an option when creating a new RDF::RDFa::Parser object. You probably want to leave this alone unless you know what you're doing.
Bundles include: rdfa, html5, html4, html32, iana, grddl, xfn.
Suggested options hashref for parsing XHTML.
Suggested options hashref for parsing HTML 4.x.
Suggested options hashref for parsing HTML5.
Suggested options hashref for parsing SVG.
Suggested options hashref for parsing Atom / DataRSS.
Suggested options hashref for parsing generic XML.
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.
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
RDF::RDFa::Parser
A reference to the XML::LibXML::Element being parsed
XML::LibXML::Element
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.
This is the equivalent of pretriple_resource, but is only called for triples with a literal object value.
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.)
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:
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.
This is called when a new CURIE prefix is discovered. The parameters passed to the callback function are:
The prefix (string, e.g. "foaf")
The expanded URI (string, e.g. "http://xmlns.com/foaf/0.1/")
The parser has support for named graphs within a single RDFa document. To switch this on, use the 'graph' option in the constructor.
The name of the attribute which indicates graph URIs is by default 'graph', but can be changed using the 'graph_attr' 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 'graph_type' to 'about', it will be treated as a URI or safe CURIE (like the 'about' attribute).
The 'graph_default' option allows you to set the default graph URI/bnode identifier.
See also http://buzzword.org.uk/2009/rdfa4/spec.
When processing Atom, if the 'atom_elements' option is switched on, RDF::RDFa::Parser will treat <feed> and <entry> elements specially. This is similar to the special support for <head> and <body> mandated by the XHTML+RDFa Recommendation. Essentially <feed> and <entry> elements are assumed to have an imaginary "about" attribute which has its value set to a brand new blank node.
If the 'atom_parser' option is switched on, RDF::RDFa::Parser fully parses Atom feeds and entries, using the XML::Atom::OWL package. The two modules attempt to work together in assigning blank node identifiers consistently, etc. If XML::Atom::OWL is not installed, then this option will be silently ignored.
Generally speaking, adding RDFa attributes to elements in the Atom namespace themselves can result in some slightly muddy semantics. It's best to use an extension namespace and add the RDFa attributes to elements in that namespace. DataRSS provides a good example of this. See http://developer.yahoo.com/searchmonkey/smguide/datarss.html.
RDF::RDFa::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/RDF-RDFa-Parser/#auto_config" content="xhtml_lang=1&keywords=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:
content
<meta name="http://search.cpan.org/dist/RDF-RDFa-Parser/#auto_config" content="xhtml_lang=1;keywords=rdfa+html5+html4+html32" />
Any option allowed in the constructor may be given using auto config, except 'use_rtnlx', and of course 'auto_config' itself.
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" keywords="iana+rdfa;xml_base=2;atom_elements=1" />
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:
Is your XML well-formed?
Despite having several options for dealing with HTML+RDFa, this package uses a strict XML parser. If you need to deal with tag soup, you'll need to parse it into an XML::LibXML::Document yourself (e.g. using HTML::HTML5::Parser) and then pass the XML::LibXML::Document to this package's contructor function.
Are your namespaces set correctly?
Does your document have 'xmlns="http://www.w3.org/1999/xhtml"' on the root element? If not, some aspects of this package's behaviour may be unexpected. If you parsed the document using HTML::HTML5::Parser you may need to run it through HTML::HTML5::Sanity.
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.
XML::LibXML, RDF::Trine, HTML::HTML5::Parser, HTML::HTML5::Sanity, XML::Atom::OWL.
http://www.perlrdf.org/.
Toby Inkster <tobyink@cpan.org>.
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 2008-2010 Toby Inkster
This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
To install RDF::RDFa::Parser, copy and paste the appropriate command in to your terminal.
cpanm
cpanm RDF::RDFa::Parser
CPAN shell
perl -MCPAN -e shell install RDF::RDFa::Parser
For more information on module installation, please visit the detailed CPAN module installation guide.