Net::Z3950::PQF - Perl extension for parsing PQF (Prefix Query Format)
use Net::Z3950::PQF;
$parser = new Net::Z3950::PQF();
$node = $parser->parse('@and @attr 1=1003 kernighan @attr 1=4 unix');
print $node->render(0);
This library provides a parser for PQF (Prefix Query Format), an ugly
but precise string format for expressing Z39.50 Type-1 queries. This
format is widely used behind the scenes of Z39.50 applications, and is
also used extensively with test-harness programs such as the YAZ
command-line client, yaz-client. A few particularly misguided
souls have been known to type it by hand.
Unlike PQF itself, this module
is simple to use. Create a parser object, then pass PQF strings
into its parse() method to yield parse-trees. The trees are made
up of nodes whose types are subclasses of
Net::Z3950::PQF::Node.
and have names of the form
Net::Z3950::PQF::somethingNode. You may find it helpful to use
Data::Dumper to visualise the structure of the returned
parse-trees.
What is a PQF parse-tree good for? Not much. You can render a
human-readable version by invoking the top node's render() method,
which is probably useful only for debugging. If you want to do
anything useful, such as implementing an actual query server that
understands PQF, you'll have to walk the tree.
new()$parser = new Net::Z3950::PQF();
Creates a new parser object.
parse()
$query = '@and @attr 1=1003 kernighan @attr 1=4 unix';
$node = $parser->parse($query);
if (!defined $node) {
die "parse($query) failed: " . $parser->errmsg();
}
Parses the PQF string provided as its argument. If an error occurs,
then an undefined value is returned, and the error message can be
obtained by calling the errmsg() method. Otherwise, the top node
of the parse tree is returned.
$node2 = $parser->parse($query, "zthes"); $node3 = $parser->parse($query, "1.2.840.10003.3.13");
A second argument may be provided after the query itself. If it is provided, then it is taken to be either the name or the OID of a default attribute set, which attributes specified in the query belong to if no alternative attribute set is explicitly specified within the query. When this second argument is absent, the default attribute set is BIB-1.
errmsg()print $parser->errmsg();
Returns the last error-message generated by a failed attempt to parse a query.
The Net::Z3950::PQF::Node module.
The definition of the Type-1 query in the Z39.50 standard, the relevant section of which is on-line at http://www.loc.gov/z3950/agency/markup/09.html#3.7
The documentation of Prefix Query Format in the YAZ Manual, the relevant section of which is on-line at http://indexdata.com/yaz/doc/tools.tkl#PQF
Mike Taylor, <mike@indexdata.com>
Copyright 2004 by Index Data ApS.
This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.