NAME
CQL::Parser - compiles CQL strings into parse trees of Node subtypes.
SYNOPSIS
use CQL::Parser;
my $parser = CQL::Parser->new();
my $root = $parser->parse( $cql );
DESCRIPTION
CQL::Parser provides a mechanism to parse Common Query Language (CQL)
statements. The best description of CQL comes from the CQL homepage at
the Library of Congress <
http://www.loc.gov/z3950/agency/zing/cql/>
CQL is a formal language for representing queries to information
retrieval systems such as web indexes, bibliographic catalogs and museum
collection information. The CQL design objective is that queries be
human readable and human writable, and that the language be intuitive
while maintaining the expressiveness of more complex languages.
A CQL statement can be as simple as a single keyword, or as complicated
as a set of compoenents indicating search indexes, relations, relational
modifiers, proximity clauses and boolean logic. CQL::Parser will parse
CQL statements and return the root node for a tree of nodes which
describes the CQL statement. This data structure can then be used by a
client application to analyze the statement, and possibly turn it into a
query for a local repository.
Each CQL component in the tree inherits from CQL::Node and can be one of
the following: CQL::AndNode, CQL::NotNode, CQL::OrNode, CQL::ProxNode,
CQL::TermNode, CQL::PrefixNode. See the documentation for those modules
for their respective APIs.
Here are some examples of CQL statements:
* george
* dc.creator=george
* dc.creator="George Clinton"
* clinton and funk
* clinton and parliament and funk
* (clinton or bootsy) and funk
* dc.creator="clinton" and dc.date="1976"
METHODS
new()
parse( $query )
Pass in a CQL query and you'll get back the root node for the CQL parse
tree. If the CQL is invalid an exception will be thrown.
parseSafe( $query )
Pass in a CQL query and you'll get back the root node for the CQL parse
tree. If the CQL is invalid, an error code from the SRU Diagnostics List
will be returned.
XCQL
CQL has an XML representation which you can generate from a CQL parse
tree. Just call the toXCQL() method on the root node you get back from a
call to parse().
ERRORS AND DIAGNOSTICS
As mentioned above, a CQL syntax error will result in an exception being
thrown. So if you have any doubts about the CQL that you are parsing you
should wrap the call to parse() in an eval block, and check $@
afterwards to make sure everything went ok.
eval {
my $node = $parser->parse( $cql );
};
if ( $@ ) {
print "uhoh, exception $@\n";
}
If you'd like to see blow by blow details while your CQL is being parsed
set $CQL::DEBUG equal to 1, and you will get details on STDERR. This is
useful if the parse tree is incorrect and you want to locate where
things are going wrong. Hopefully this won't happen, but if it does
please notify the author.
TODO
* toYourEngineHere() please feel free to add functionality and send in
patches!
THANKYOUS
CQL::Parser is essentially a Perl port of Mike Taylor's cql-java package
http://zing.z3950.org/cql/java/. Mike and IndexData were kind enough to
allow the author to write this port, and to make it available under the
terms of the Artistic License. Thanks Mike!
The CQL::Lexer package relies heavily on Stevan Little's excellent
String::Tokenizer. Thanks Stevan!
CQL::Parser was developed as a component of the Ockham project, which is
funded by the National Science Foundation. See
http://www.ockham.org for
more information about Ockham.
AUTHOR
* Ed Summers - ehs at pobox dot com
* Brian Cassidy - bricas at cpan dot org
* Wilbert Hengst - W.Hengst at uva dot nl
COPYRIGHT AND LICENSE
Copyright 2004-2009 by Ed Summers
This library is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
