XML::XQL::Query - Creates an XQL query evaluater from a XQL expression

# NAME

XML::XQL::Query - Creates an XQL query evaluater from a XQL expression

# SYNOPSIS

     use XML::XQL;

     $parser = new XML::DOM::Parser;
     $doc = $parser->parsefile ("file.xml");

     # Return all elements with tagName='title' under the root element 'book'
     $query = new XML::XQL::Query (Expr => "book/title");
     @result = $query->solve ($doc);

     # Or (to save some typing)
     @result = XML::XQL::solve ("book/title", $doc);

# DESCRIPTION

To perform XQL queries on an XML::DOM document (or, in the future, on other XML storage structures), you first have to create an XML::XQL::Query object and pass it a valid XQL query expression. You can then perform queries on one or more documents by calling the solve() method.

# XML::XQL::Query constructor

Usage, e.g:

     $query = new XML::XQL::Query(
    	Expr => "book/author",
    	Func => [ myfunc => \&my_func,		# define 2 functions
    		  myfunc2 => \&my_func2 ],
    	FuncArgCount => [ myfunc2 => [2, -1] ], # myfunc2 has 2 or more args
    	AllowedOutSideSubquery => [ myfunc => 1 ],
    	ConstFunc => [ myfunc2 => 1],
    	CompareOper => [ mycmp => \&mycmp ],	# define comparison operator
    	q => "str");				# use str// as string delim

Expr => STRING

  The query expression to be evaluated.

NodeQuery => BOOLEAN

  If set to 1, the query is a Node Query as opposed to a Full Query (which is the default.) A node query is a query that is only capable of returning Nodes. A full query is capable of returning Node values and non-Node values. Non-Node values include XML Primitives, element type names, namespace URI's, concatenated text nodes, and node type names. The distinction is significant because node queries may appear as XSL match and select patterns, while full queries have use in other applications. The difference between the two forms of queries is trivial and exists only as constraints on the syntax of node queries. Node queries may contain nested full queries.

Func => [ FUNCNAME => FUNCREF, ...]

  Defines one or more functions. FUNCNAME is the name as used in the query expression. FUNCREF can be either a function reference like \&my_func or an anonymous sub. See also: defineFunction

Method => [ FUNCNAME => FUNCREF, ...]

  Defines one or more methods. FUNCNAME is the name as used in the query expression. FUNCREF can be either a function reference like \&my_func or an anonymous sub. See also: defineMethod

FuncArgCount => [ FUNCNAME => ARGCOUNT, ...]

  Defines the number of arguments for one or more functions or methods. FUNCNAME is the name as used in the query expression. See also: defineFunction and defineMethod

AllowedOutsideSubquery => [ FUNCNAME => BOOLEAN, ...]

  Defines whether the specified function or method is allowed outside subqueries. FUNCNAME is the name as used in the query expression. See also: defineFunction and defineMethod

ConstFunc => [ FUNCNAME => BOOLEAN, ...]

  Defines whether the function (not method!) is a "constant" function. FUNCNAME is the name as used in the query expression. See Constant Function Invocations for a definition of "constant" See also: defineFunction and defineMethod

CompareOper => [ OPERNAME => FUNCREF, ...]

  Defines the comparison operator with the specified OPERNAME, e.g. if OPERNAME is "contains", you can use "$contains$" in the query. See also: defineComparisonOperators

q => TOKEN

  Defines the q// token. See also: defineTokenQ

qq => TOKEN

  Defines the qq// token. See also: defineTokenQQ

Error => FUNCREF

  Defines the function that is called when errors occur during parsing the query expression. The default function prints an error message to STDERR.

Debug => FLAGS

  Sets the debug level for the Yapp parser that parses the query expression. Default value is 0 (don't print anything). The maximum value is 0x17, which prints a lot of stuff. See the Parse::Yapp manpage for the meaning of the individual bits.

Reserved hash keys

  Users may add their own (key, value) pairs to the Query constructor. Beware that the key 'Tree' is used internally.

# XML::XQL::Query methods

solve (INPUT_LIST...)

  Note that solve takes a list of nodes which are assumed to be in document order and must belong to the same document. E.g:

       $query = new XML::XQL::Query (Expr => "doc//book");
       @result = $query->solve ($doc);
       @result2 = $query->solve ($node1, $node2, $node3);

The following functions are also available at the query level, i.e. when called on a Query object they only affect this Query and no others:

     defineFunction, defineMethod, defineComparisonOperators,
     defineTokenQ, defineTokenQQ

See Global functions for details. Another way to define these features for a particular Query is by passing the appropriate values to the XML::XQL::Query constructor.

# SEE ALSO

XML::XQL for general information about the XML::XQL module

XML::XQL::Tutorial which describes the XQL syntax

Last updated: Wed Feb 23 13:37:41 2000