29. A system for executing a function included in an XPath-based query requesting data from a markup language document stored in a database, the markup language document organized hierarchically into nodes, the system comprising: a computer having at least a processor and a memory; a compiler module, operating on said computer, for generating a plan for identifying nodes of the markup language document satisfying the XPath- based query, the XPath-based query including a an XPath-based built-in function that operates within a particular context of the markup language document during execution of the XPath-based query; and an execution module, operating on said computer, for executing the plan to identify nodes of the markup language document satisfying the XPath-based query, obtaining values corresponding to identified nodes of the markup language document, associating said values with the identified nodes, and executing the XPath- based built-in function included in the XPath-based query with said values and identified nodes.
29. A system for executing a function included in an XPath-based query requesting data from a markup language document stored in a database, the markup language document organized hierarchically into nodes, the system comprising: a computer having at least a processor and a memory; a compiler module, operating on said computer, for generating a plan for identifying nodes of the markup language document satisfying the XPath- based query, the XPath-based query including a an XPath-based built-in function that operates within a particular context of the markup language document during execution of the XPath-based query; and an execution module, operating on said computer, for executing the plan to identify nodes of the markup language document satisfying the XPath-based query, obtaining values corresponding to identified nodes of the markup language document, associating said values with the identified nodes, and executing the XPath- based built-in function included in the XPath-based query with said values and identified nodes. 30. The system of claim 29 , wherein the markup language comprises Extensible Markup Language (XML).