Ubuntu Manpage: XML::TreePuller - Pull interface to work with XML document fragments

Provided by: libxml-treepuller-perl_0.1.2-1_all

NAME

       XML::TreePuller - Pull interface to work with XML document fragments

SYNOPSIS

         use XML::TreePuller;

         $pull = XML::TreePuller->new(location => '/what/ever/filename.xml');
         $pull = XML::TreePuller->new(location => 'http://urls.too/data.xml');
         $pull = XML::TreePuller->new(IO => \*FH);
         $pull = XML::TreePuller->new(string => '<xml/>');

         #parse the document and return the root element
         #takes same arguments as new()
         $element = XML::TreePuller->parse(%ARGS);

         $pull->reader; #return the XML::LibXML::Reader object

         $pull->iterate_at('/xml', 'short'); #read the first part of an element
         $pull->iterate_at('/xml', 'subtree'); #read the element and subtree

         while($element = $pull->next) { }

         $element->name;
         $element->text; #fetch text for the element and all children
         $element->attribute('attribute_name'); #get attribute value
         $element->attribute; #returns hashref of attributes
         $element->get_elements; #return all child elements
         $element->get_elements('element/path'); #elements from path
         $element->xpath('/xml'); #search using a XPath

ABOUT

This module implements a tree oriented XML pull processor providing fast and convenient
unmarshalling of extremely large XML documents serially. Unmarshalling means the module is
intended to turn the XML document into datastructures, not transform it. Tree oriented
means the data is returned from the engine as a tree of data replicating the structure of
the original XML document. Pull processor means you sequentially ask the engine for more
data (the opposite of SAX). This engine also supports breaking the document into fragments
so the trees are small enough to fit into RAM.

Features
High speed
This framework has been benchmarked to process XML between 1 meg/sec and 70 meg/sec in
real world scenarios using the high level interface.

Work with documents too big to fit into RAM
The interface is nearly identical for large documents and small documents.

High level
The document is mapped to a high level XML element class that is easy to use.

Low level
If you need lower level access to the XML document you can treat the element class as
a set of arrays representing the structure of your document or you can work with the
XML::LibXML::Reader instance directly.

Justification
"Another XML processing scheme? Why don't you create a new template parsing framework to
go with it!?" -- If I had a trillion dollars for every time I've heard this I could bail
out the US Government (as of Apr 26, 2010 that is). When I set out to create the
replacement for Parse::MediaWikiDump I started by benchmarking the performance of existing
XML processing frameworks (XML::SAX (all of them), XML::Parser, and higher level
frameworks such as XML::Twig). The results of my research was that there exists no very
fast pull oriented high level framework for processing XML.

I set about building MediaWiki::DumpFile using a base of XML::LibXML::Reader and
XML::CompactTree; I wound up with a reconfigurable XML processing engine that I rather
liked so I decided to publish it on CPAN.

STATUS

       This software is currently ALPHA quality - the only known use is MediaWiki::DumpFile which
       is itself becoming tested in production. The API is not stable and there may be bugs:
       please report success and failure to the author below.

XML::TreePuller

   METHODS
       new The constructor for this class returns an instance of itself; all arguments are passed
           straight on to XML::LibXML::Reader when it is constructed. See the documentation for a
           full specification of what you can use but for quick reference:

           new(location => '/what/ever/filename.xml');
           new(location => 'http://urls.work.too/data.xml');
           new(string => $xml_data);
           new(IO => \*FH);
       parse
           This method takes the same arguments as new() but parses the entire document into an
           element and returns it; you can use this if you don't need to break the document into
           chunks.

       iterate_at
           This method allows you to control the configuration of the processing engine; you
           specify two arguments: a path to an XML element and an instruction. The engine will
           move along node by node through the document and keep track of the full path to the
           current element.  The combination of the current path of the XML document in the
           reader and the instruction to use will cause instances of XML::TreePuller::Element to
           be available from the "next" method.

           If iterate_at() is never called then the entire document will be read into a single
           element at the first invocation of next().

           iterate_at('/path/to/element' => 'short');
               When the path of the current XML element matches the path specified the "next"
               method will return an instance of XML::TreePuller::Element that holds any
               attributes and will contain textual data up to the start of another element; there
               will be no child elements in this element.

           iterate_at('/ditto' => 'subtree');
               When the path of the current XML element matches the path specified the "next"
               method will return an instance of XML::TreePuller::Element that holds the
               attributes for the element and all of the element textual data and child elements.

       next
           This method is the iterator for the processing system. Each time an instruction is
           matched it will return an instance of XML::TreePuller::Element. When called in scalar
           context returns a reference to the next available element or undef when no more data
           is available. When called in list context it returns a two item list with the first
           item being the path to the node that was matched and the second item being the next
           available element; returns an empty list when there is no more data to be processed.

           The returned path will always be a full path in the document starting at the root
           element and ending in the element that ultimately matched.

       reader
           Returns the instance of XML::LibXML::Reader that we are using to parse the XML
           document. You can move the cursor of the reader if you want but keep this in mind: if
           you move the cursor of the reader to an element in the document that is at a higher
           level than the reader was sitting at when you moved it then the reader must move the
           cursor to an element that was at the same depth in the document as it was at the
           start; this may cause some parts of the document to be thrown out that you are not
           expecting.

XML::TreePuller::Element

This class is how you access the data from XML::TreePuller. XML::TreePuller::Element is
implemented as a set of methods that operate on arrays as returned by XML::CompactTree;
you are free to work with XML::TreePuller::Element objects just as you would work with
data returned from XML::CompactTree::readSubtreeToPerl() and such.

METHODS
name
Returns the name of the element as a string

text
Returns the text stored in the element and all subelements as a string; returns an
empty string if there is no text

attribute
If called with out any arguments returns a hash reference containing the attribute
names as keys and the attribute values as the data. If called with an argument returns
the value for the attribute by that name or undef if there is no attribute by that
name.

get_elements
Searches this element for any child elements as matched by the path supplied as an
argument; the path is relative to the current element. The path is of the format
'element1/element2/element3' where each element name is separated by a forward slash
and there are no trailing or leading forward slashes. If no path is specified it
returns all of the child elements for the current element.

If called in scalar context returns the first element that matches the path; if called
in array context returns a list of all elements that matched.

xpath
Perform an XPath query on the element and return the results; if called in list
context you'll get all of the elements that matched. If called in scalar context
you'll get the first element that matched. XPath support is currently EXPERIMENTAL.

The XPath query is rooted at the element so you must include the current element name
as part of the path if you are specifying an absolute path to a subelement.

IMPROVING PERFORMANCE

       First of all if you want to improve the throughput of this XML processing system be sure
       to install XML::CompactTree::XS - once installed this module is used automatically and
       drastically improves overall performance of unmarshalling the XML from the document (this
       does not involve XML::TreePuller::Element).

       Secondly there are a number of ways to solve problems with this module, see
       XML::TreePuller::CookBook::Performance for information.

LIMITATIONS

       •   This module is not XML compliant though it is built from XML compliant components.
           There may be unexpected behavior compared to proper XML behavior and if this is
           encountered please open a bug report.

       •   XPath support is EXPERIMENTAL (even more so than the rest of this module)

       •   There is only support for elements, text in elements, and CDATA blocks - other
           features of XML are not part of the API and are not tested but may bleed through from
           the underlying modules used to build this system. If you have an idea on how to add
           support for these extra features the author is soliciting feedback and patches.

       •   Things are pretty arbitrary right now as this module started life as the heart of
           MediaWiki::DumpFile; it would be nice to bring in more formal XML processing concepts.

ATTRIBUTION

       With out the following people this module would not be possible:

       Andrew Rodland
           My Perl mentor and friend, his influence has helped me everywhere.

       Petr Pajas
           As the maintainer of XML::LibXML and creator of XML::CompactTree this module would not
           be possible with out building on his great work.

       Michel Rodriguez
           For creating Tree::XPathEngine which made adding XPath support a one day exercise.

AUTHOR

       Tyler Riddle, "<triddle at cpan.org>"