NAME
HTML::Untemplate - web scraping assistant
VERSION
version 0.019
DESCRIPTION
Suppose you have a set of HTML documents generated by populating the
same template with the data from some kind of database.
HTML::Untemplate is a set of command-line tools ("xpathify",
"untemplate") and modules (HTML::Linear and it's dependencies) which
assist in original data retrieval.
This process is also known as wrapper induction
<https://en.wikipedia.org/wiki/Wrapper_(data_mining)>.
To achieve this goal, HTML tree nodes are presented as XPath/content
pairs. HTML documents linearized this way can be easily inspected
manually or with a diff tool. Please refer to "EXAMPLES".
Despite being named similarly to HTML::Template, this distribution is
not directly related to it. Instead, it attempts to reverse the
templating action, whatever the template agent used.
Why?
Suppose you have a CMS. Typical CMS works roughly as this (data flows
bottom-down):
RDBMS
scripting language
HTML
HTTP server
(...)
HTTP agent
layout engine
screen
user
Consider the first 3 steps: RDBMS => scripting language => HTML
This is "applying template".
Now, consider this: HTML => scripting language => RDBMS
I would call that "un-applying template", or "untemplate" :)
The practical application of this set of tools is to assist in creation
of web scrappers.
A similar (however completely unrelated) approach is described in the
paper XPath-Wrapper Induction for Data Extraction
<http://www.coltech.vnu.edu.vn/~thuyhq/papers/10_Khanh_Cuong_thuy_4288a
150.pdf>.
Human-readability
Consider the following HTML node address representations:
* 0.1.3.0.0.4.0.0.0.2 (HTML::TreeBuilder internal address
representation);
* /html/body/div[4]/div/div[1]/table[2]/tr/td/ul/li[3] (HTML::Linear,
strict);
* //td[1]/ul[1]/li[3] (HTML::Linear, strict, shrink);
*
/html/body[@class='section_home']/div[@id='content_holder'][1]/div[@i
d='content']/div[@id='main']/table[@class='content_table'][2]/tr/td/u
l/li[@class='rss_content rss_content_col'][2] (HTML::Linear,
non-strict);
* //li[@class='rss_content rss_content_col'][2] (HTML::Linear,
non-strict, shrink).
They all point to the same node, however, their verbosity/readability
vary. The strict mode specifies tag names and positions only. Disabling
strict will use additional data from CSS selectors. Shrink mode
attempts to find the shortest XPath unique for every node (/html/body
is shared among almost all nodes, thus is likely to be irrelevant).
EXAMPLES
xpathify
The xpathify tool flatterns the HTML tree into key/value list:
<!DOCTYPE html>
<html>
<head>
<title>Hello HTML</title>
</head>
<body>
<h1>Hello World!</h1>
<p>This is a sample HTML</p>
Beware!
<p>HTML is <b>not</b> XML!</p>
Have a nice day.
</body>
</html>
Becomes:
(HTML block)
The keys are in XPath format, while the values are respective content
from the HTML tree. Theoretically, it could be possible to reassemble
the HTML tree from the flat key/value list this tool generates.
untemplate
The untemplate tool flatterns a set of HTML documents using the
algorithm from xpathify. Then, it strips the shared key/value pairs.
The "rest" is composed of original values fed into the template engine.
And this is how the result actually looks like with some simple
real-world examples (quotes 1839 <http://bash.org/?1839> and 2486
<http://bash.org/?2486> from bash.org):
(HTML block)
MODULES
May be used to serialize/flattern HTML documents by your own:
* HTML::Linear - represent HTML::Tree as a flat list
* HTML::Linear::Element - represent elements to populate HTML::Linear
* HTML::Linear::Path - represent paths inside HTML::Tree
REFERENCES
* Wrapper (data mining)
<https://en.wikipedia.org/wiki/Wrapper_(data_mining)>
* XPath-Wrapper Induction for Data Extraction
<http://www.coltech.vnu.edu.vn/~thuyhq/papers/10_Khanh_Cuong_thuy_428
8a150.pdf>
* Extracting Data from HTML Using TreeBuilder Node IDs
<http://secondthought.org/notes/nodeIdProbabilities.html>
* Web Scraping Made Simple with SiteScraper
<http://sitescraper.googlecode.com/files/sitescraper.pdf>
SEE ALSO
* HTML::Similarity
* Template::Extract
* XML::DifferenceMarkup
* XML::XSH2
AUTHOR
Stanislaw Pusep <stas@sysd.org>
COPYRIGHT AND LICENSE
This software is copyright (c) 2014 by Stanislaw Pusep.
This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.