Perl-style xml objects
use XML::Grove;
# Basic parsing and grove building
use XML::Grove::Builder;
use XML::Parser::PerlSAX;
$grove_builder = XML::Grove::Builder->new;
$parser = XML::Parser::PerlSAX->new ( Handler => $grove_builder );
$document = $parser->parse ( Source => { SystemId => 'filename' } );
# Creating new objects
$document = XML::Grove::Document->new ( Contents => [ ] );
$element = XML::Grove::Element->new ( Name => 'tag',
Attributes => { },
Contents => [ ] );
# Accessing XML objects
$tag_name = $element->{Name};
$contents = $element->{Contents};
$parent = $element->{Parent};
$characters->{Data} = 'XML is fun!';
XML::Grove is a tree-based object model for accessing the information set of parsed or stored \s-1XML\s0, \s-1HTML\s0, or \s-1SGML\s0 instances. XML::Grove objects are Perl hashes and arrays where you access the properties of the objects using normal Perl syntax:
$text = $characters->{Data};
There are several ways for groves to come into being, they can be read from a file or string using a parser and a grove builder, they can be created by your Perl code using the `\*(C`new()\*(C'' methods of XML::Grove::Objects, or databases or other sources can act as groves.
The most common way to build groves is using a parser and a grove builder. The parser is the package that reads the characters of an \s-1XML\s0 file, recognizes the \s-1XML\s0 syntax, and produces ``events'' reporting when elements (tags), text (characters), processing instructions, and other sequences occur. A grove builder receives (``consumes'' or ``handles'') these events and builds XML::Grove objects. The last thing the parser does is return the XML::Grove::Document object that the grove builder created, with all of it's elements and character data.
The most common parser and grove builder are XML::Parser::PerlSAX (in libxml-perl) and XML::Grove::Builder. To build a grove, create the grove builder first:
$grove_builder = XML::Grove::Builder->new;
Then create the parser, passing it the grove builder as it's handler:
$parser = XML::Parser::PerlSAX->new ( Handler => $grove_builder );
This associates the grove builder with the parser so that every time you parse a document with this parser it will return an XML::Grove::Document object. To parse a file, use the `\*(C`Source\*(C'' parameter to the `\*(C`parse()\*(C'' method containing a `\*(C`SystemId\*(C'' parameter (\s-1URL\s0 or path) of the file you want to parse:
$document = $parser->parse ( Source => { SystemId => 'kjv.xml' } );
To parse a string held in a Perl variable, use the `\*(C`Source\*(C'' parameter containing a `\*(C`String\*(C'' parameter:
$document = $parser->parse ( Source => { String => $xml_text } );
The following are all parsers that work with XML::Grove::Builder:
XML::Parser::PerlSAX (in libxml-perl, uses XML::Parser) XML::ESISParser (in libxml-perl, uses James Clark's `nsgmls') XML::SAX2Perl (in libxml-perl, translates SAX 1.0 to PerlSAX)
Most parsers supply more properties than the standard information set below and XML::Grove will make available all the properties given by the parser, refer to the parser documentation to find out what additional properties it may provide.
Although there are not any available yet (August 1999), PerlSAX filters can be used to process the output of a parser before it is passed to XML::Grove::Builder. XML::Grove::PerlSAX can be used to provide input to PerlSAX filters or other PerlSAX handlers.
The properties provided by parsers are available directly using Perl's normal syntax for accessing hashes and arrays. For example, to get the name of an element:
$element_name = $element->{Name};
By convention, all properties provided by parsers are in mixed case. `\*(C`Parent\*(C'' properties are available using the `\*(C`Data::Grove::Parent\*(C'' module.
The following is the minimal set of objects and their properties that you are likely to get from all parsers:
The Document object is parent of the root element of the parsed \s-1XML\s0 document.
An array containing the root element.
A document's `Contents' may also contain processing instructions, comments, and whitespace.
Some parsers provide information about the document type, the \s-1XML\s0 declaration, or notations and entities. Check the parser documentation for property names.
The Element object represents elements from the \s-1XML\s0 source.
The parent object of this element.
A string, the element type name of this element
A hash of strings or arrays
An array of elements, characters, processing instructions, etc.
In a purely minimal grove, the attributes of an element will be plain text (Perl scalars). Some parsers provide access to notations and entities in attributes, in which case the attribute may contain an array.
The Characters object represents text from the \s-1XML\s0 source.
The parent object of this characters object
A string, the characters
The \s-1PI\s0 object represents processing instructions from the \s-1XML\s0 source.
The parent object of this \s-1PI\s0 object.
A string, the processing instruction target.
A string, the processing instruction data, or undef if none was supplied.
In addition to the minimal set of objects above, XML::Grove knows about and parsers may provide the following objects. Refer to the parser documentation for descriptions of the properties of these objects.
XML::Grove:: ::Entity::External External entity reference ::Entity::SubDoc External SubDoc reference (SGML) ::Entity::SGML External SGML reference (SGML) ::Entity Entity reference ::Notation Notation declaration ::Comment <!-- A Comment --> ::SubDoc A parsed subdocument (SGML) ::CData A CDATA marked section ::ElementDecl An element declaration from the DTD ::AttListDecl An element's attribute declaration, from the DTD
XML::Grove by itself only provides one method, new(), for creating new XML::Grove objects. There are Data::Grove and XML::Grove extension modules that give additional methods for working with XML::Grove objects and new extensions can be created as needed. `\*(C`new\*(C'' creates a new XML::Grove object with the type \s-1OBJECT\s0, and with the initial \s-1PROPERTIES\s0. \s-1PROPERTIES\s0 may be given as either a list of key-value pairs, a hash, or an XML::Grove object to copy. \s-1OBJECT\s0 may be any of the objects listed above.
This is a list of available extensions and the methods they provide (as of Feb 1999). Refer to their module documentation for more information on how to use them.
XML::Grove::AsString as_string return portions of groves as a string attr_as_string return an element's attribute as a string
XML::Grove::AsCanonXML as_canon_xml return XML text in canonical XML format
XML::Grove::PerlSAX parse emulate a PerlSAX parser using the grove objects
Data::Grove::Parent root return the root element of a grove rootpath return an array of all objects between the root element and this object, inclusive
Data::Grove::Parent also adds `C<Parent>' and `C<Raw>' properties to grove objects.
Data::Grove::Visitor accept call back a subroutine using an object type name accept_name call back using an element or tag name children_accept for each child in Contents, call back a sub children_accept_name same, but using tag names attr_accept call back for the objects in attributes
XML::Grove::IDs get_ids return a list of all ID attributes in grove
XML::Grove::Path at_path $el->at_path('/html/body/ul/li[4]')
XML::Grove::Sub filter run a sub against all the objects in the grove
The class `\*(C`XML::Grove\*(C'' is the superclass of all classes in the XML::Grove module. `\*(C`XML::Grove\*(C'' is a subclass of `\*(C`Data::Grove\*(C''.
If you create an extension and you want to add a method to all XML::Grove objects, then create that method in the XML::Grove package. Many extensions only need to add methods to XML::Grove::Document and/or XML::Grove::Element.
When you create an extension you should definitly provide a way to invoke your module using objects from your package too. For example, XML::Grove::AsString's `\*(C`as_string()\*(C'' method can also be called using an XML::Grove::AsString object:
$writer= new XML::Grove::AsString; $string = $writer->as_string ( $xml_object );
Ken MacLeod, [email protected]
perl\|(1), XML::Grove\|(3)
Extensible Markup Language (\s-1XML\s0) <http://www.w3c.org/XML>