Template Folding for XPath

We discuss query evaluation for XML-based server systems where the same query is evaluated on every incoming XML message. In a typical scenario, many of the incoming messages will be highly similar to each other. Current XML query evaluators reevaluate the query from scratch on every message. We call substructures that occur in many input documents template fragments, and introduce a novel template folding method that allows to move the work of evaluating the query on recurring document substructures from the query execution engine into the query compiler. Similar to constant folding, our method avoids run-time evaluation of intermediate results whose value only depends on information that is already available at compile time. For XPath location paths, we propose a representation for such invariant intermediate results, and show how it can be incorporated into query execution plans. Such augmented execution plans improve query performance when evaluating the same query on subsequent i...

• Type: Conference
• Year: 2006
• Where: XIMEP
• Authors: Carl-Christian Kanne, Guido Moerkotte
• Keywords: Database, Query Evaluation, Query Execution, XIMEP 2006, XML Query Evaluators