NAME
WWW::Search - Virtual base class for WWW searches
DESCRIPTION
This class is the parent for all access method supported by the WWW::Search library.
Search results are limited and there is a pause between each request for results to avoid overloading either the client or the server.
Sample program
Using the library should be straightforward: Here's a sample program:
my($search) = new WWW::Search::AltaVista;
$search->native_query(WWW::Search::escape_query($query));
my($result);
while ($result = $search->next_result()) {
print $result->url, "\n";
};Results are objects of WWW::SearchResult (see WWW::SearchResult) .
SEE ALSO
For more details see LWP.
METHODS AND FUNCTIONS
new
To create a new WWW::Search, call $search = new WWW::Search::SearchEngineName(); where SearchEngineName is replaced with a particular search engine. For example: $search = new WWW::Search::AltaVista();
The next step is usually: $search->native_query('search-engine-specific query string');
native_query
Specify a query to the current search object. The query must be escaped; call "escape_query" in WWW::Search to escape a plain query. Doesn't actually begin the search until results or next_result is called.
Example: $search->native_query('search-engine-specific query string');
The next step is usually:
@results = $search->results();or
while ($result = $search->next_result()) {
# do_something;
};results
Return all the results of a query as a reference to array of SearchResult objects.
Example: @results = $search->results(); foreach $result (@results) { print $result->url(), "\n"; };
next_result
Return each result of a query as a SearchResult object.
Example: while ($result = $search->next_result()) { print $result->url(), "\n"; };
seek_result($offset)
Set which result next_result should return (like lseek in Unix). Results are zero-indexed.
The only guaranteed valid offset is 0 which will replay the results from the beginning. In particular, seeking past the end of the current cached results probably won't do what you might think it should.
Results are cached, so this doesn't re-issue the query or cause IO (unless you go off the end of the results). To re-do the query, create a new search object.
Example: $search->seek_result(0);
maximum_to_retrieve
The maximum number of hits to return (approximately). Queries resulting in more than this many hits will return the first hits, up to this limit.
Defaults to 500.
Example: $max = $seach->maximum_to_retrieve(100);
escape_query
Escape a query. Before queries are made special characters must be escaped so that a proper URL can be formed.
This is like escaping a URL but "+" is a protected character and spaces are converted to "+"'s.
Example: $escaped = Search::escape_query('+lsam +replication'); (Returns "%22lsam+replication%22").
See also unescape_query.
unescape_query
Unescape a query. See escape_query for details.
Example: $unescaped = Search::unescape_query('%22lsam+replication%22'); (Returns "+lsam +replication").
See also unescape_query.
setup_search (PRIVATE)
This internal routine does generic Search setup. It calls native_setup_search to do back-end specific setup.
setup_user_agent (PRIVATE, NOT A METHOD)
This internal routine does setup for a user-agent for dervived classes that use the web.
user_agent_delay (PRIVATE)
Derived classes should call this between requests to remote servers to avoid overloading them with many, fast back-to-back requests.
retrieve_some (PRIVATE)
An internal routine to interface with native_retrieve_some. Checks for overflow.
IMPLEMENTING NEW BACK-ENDS
WWW::Search supports back-ends to separate search engines. Each back-end is implemented as a subclass of WWW::Search. WWW::Search::AltaVista provides a good sample back-end.
A back-end usually has two routines, native_retrieve_some and native_setup_search.
native_retrieve_some is the core of a back-end. It will be called periodically to fetch URLs. Each call it should fetch a page with about 10 or so hits and add them to the cache. It should return the number of hits found or undef when there are no more hits.
Internally, native_retrieve_some typically will parse the HTML, extract the links and descriptions, then find the ``next'' button and save the URL. See the code for the AltaVista implementation for an example.
native_setup_search is invoked before the search. It is passed a single argument: the escaped, native version of the query.
The front- and back-ends share a single object (a hash) The back-end can change any hash element beginning with underscore, and {response} (an HTTP::Response code) and {cache} (the array of WWW::SearchResult objects caching all results).
If you implement a new back-end, please let the authors know.
AUTHOR
WWW::Search is written by John Heidemann, <johnh@isi.edu>.
COPYRIGHT
Copyright (c) 1996 University of Southern California. All rights reserved.
Redistribution and use in source and binary forms are permitted provided that the above copyright notice and this paragraph are duplicated in all such forms and that any documentation, advertising materials, and other materials related to such distribution and use acknowledge that the software was developed by the University of Southern California, Information Sciences Institute. The name of the University may not be used to endorse or promote products derived from this software without specific prior written permission.
THIS SOFTWARE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.