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()¶
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.
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.