Net::Z3950::PQF::Node - Abstract class for nodes in a PQF parse tree
$node = new Net::Z3950::PQF::TermNode('unix');
$node->isa("Net::Z3950::PQF::Node") or die "oops";
This module implements the types for the nodes that make up a PQF parse tree. Each such concrete type is a subclass of the abstract base class Net::Z3950::Node, and has a type whose name is of the form Net::Z3950::PQF::somethingNode.
The following node types are defined:
TermNodeRepresents an actual query term such as brian, "brian" or "Brian W. Kernighan".
The term is accompanied by zero or more attributes, each of which is a triple represented by a reference to a three-element array. Each such array consists of an attribute set identifier which may be either an OID or a short descriptive string, an integer type, and a value which may be either an integer or a string.
RsetNodeRepresents a result-set node, a reference to the name of a prior result set. The result-set name is accompanied by zero or more attributes as above.
AndNodeRepresents an AND node with two sub-nodes.
OrNodeRepresents an OR node with two sub-nodes.
NotNodeRepresents a NOT node with two sub-nodes. In the Z39.50 Type-1 query, and hence in PQF, NOT is a binary AND-NOT operator rather than than a unary negation operator.
ProxNodeRepresents a proximity node with two subnodes and five parameters:
exclusion: a boolean indicating whether the condition indicated by the other parameters should be inverted.
distance: an integer indicating the number of units that may separate the fragments identified by the subnodes.
ordered: a boolean indicating whether the elements indicated by the subnodes are constrained to be in the same order as the subnodes themselves.
relation: indicates the relation required on the specified distance in order for the condition to be satisfied.
unit: a short string indicating the units of proximity (word, sentence, etc.)
Except where noted, the methods described below are defined for all of the concrete node types.
$term1 = new Net::Z3950::PQF::TermNode('brian', [ "bib-1", 1, 1003 ]);
$term2 = new Net::Z3950::PQF::TermNode('unix', [ "bib-1", 1, 4 ]);
$and = new Net::Z3950::PQF::AndNode($term1, $term2);
Creates a new node object of the appropriate type. It is not possible to instantiate the abstract node type, Net::Z3950::PQF::Node, only its concrete subclasses.
The parameters required are different for different node types:
TermNodeThe first parameter is the actual term, and the remainder are attributes, each represented by a triple of [ attribute-set, type, value ].
AndNode, OrNode, NotNodeThe two parameters are nodes representing the subtrees.
ProxNodeThe seven parameters are, in order: the two nodes representing the subtrees, and the five parameters exclusion, distance, ordered, relation and unit.
$node->render(0);
Renders the contents of the tree rooted at the specified node, indented to a level indicated by the parameter. This output is in a human-readable form that is useful for debugging but probably not much else.
$node->toSimpleServer();
Transforms the contents of the tree rooted at the specified node, returning a correpsonding tree of the Perl structures produced by the Net::Z3950::SimpleServer module and passed as the {RPN} argument to search handlers. This emulation is useful for testing code that expects to receive queries in that format.
This module is part of the Net::Z3950::PQF distribution. The copyright, authorship and licence are all as for the distribution.
