Version 0.3, 2005-07-04, http://www.neilvandyke.org/webscraperhelper/
by
Neil W. Van Dyke
<neil@neilvandyke.org>
Copyright © 2004 - 2005 Neil W. Van Dyke. This program is Free
Software; you can redistribute it and/or modify it under the terms of the
GNU Lesser General Public License as published by the Free Software
Foundation; either version 2.1 of the License, or (at your option) any
later version. This program is distributed in the hope that it will be
useful, but without any warranty; without even the implied warranty of
merchantability or fitness for a particular purpose. See
<http://www.gnu.org/copyleft/lesser.html> for details. For
other license options and consulting, contact the author.
WebScraperHelper is intended as a programmer's aid for crafting SXPath queries to extract information (e.g., news items, prices) from HTML Web pages that have been parsed by HtmlPrag. The current version of WebScraper accepts an example SXML (or SHTML) document and an example “goal” subtree of the document, and yields up to three different SXPath queries. A generated query can often be incorporated into a Web-scraping program as-is, for extracting information from documents with very similar formatting. Generated queries can also be used as starting points for hand-crafted queries.
For example, given the SXML document doc:
(define doc
'(*TOP* (html (head (title "My Title"))
(body (@ (bgcolor "white"))
(p "Summary: This is a document.")
(div (@ (id "ResultsSection"))
(h2 "Results")
(p "These are the results.")
(table (@ (id "ResultTable"))
(tr (td (b "Input:"))
(td "2 + 2"))
(tr (td (b "Output:"))
(td "Four")))
(p "Lookin' good!"))))))
evaluating the expression
(webscraperhelper '(td "Four") doc)
will display generated queries like:
Absolute SXPath: (html body div table (tr 2) (td 2))
Absolute SXPath with IDs: (html body
(div (@ (equal? (id "ResultsSection"))))
(table (@ (equal? (id "ResultTable"))))
(tr 2) (td 2))
Relative SXPath with IDs: (// (table (@ (equal? (id "ResultTable"))))
(tr 2) (td 2))
The queries can then be compiled with the sxpath procedure of the
SXPath library:
(define query
(sxpath '(// (table (@ (equal? (id "ResultTable"))))
(tr 2) (td 2))))
(query doc) => ((td "Four"))
This version of WebScraperHelper requires R5RS, SRFI-11, and SRFI-16.
WebScraperHelper also comes with an advertising jingle (with apologies to greasy ground bovine additive Americana):
WebScraperHelper
helps a programmer
scrape the
Web a great deal!
In this version, the `interactive” interface is a procedure intended to be invoked manually from a REPL.
Displays some XPath queries yielding SXML goal from document sxml.
goal is the desired SXML element node.
sxml is the document in SXML First Normal Form (1NF). Some nested nodelists emitted by SXML transformation tools, such as
(a ((@ (x "y")))instead of(a (@ (x "y")), are not permitted.The optional ids is a list of name symbols for element attributes that can be treate as unique identifiers. If ids is not given, then the default is
'(id). (Note: Since some Scheme implementations have case-insensitive readers, but SXML is case-sensitive, you may have to use(list (string->symbol "foo") (string->symbol "bar"))instead of'(foo bar).)
The programmatic interface, such as it is, will likely change substantially in a future version, as new ways of generating queries are implemented. The following procedures are therefore exposed only for tinkering, and are not really documented.
Yields a wsh-path to goal within sxml, or
#fif no path could be found. The yielded path might share structure with sxml.
Translate a wsh-path to various SXPath queries. The yielded SXPath query lists should be considered immutable, as they might share structure with the original SXML from which path was generated, or multiple queries might share structure with each other.