1. Streaming XPath Engine Oleg Slezberg Amruta Joshi

2. Overview Motivation –Querying Streaming XML –XPath Challenges (predicates, //, nesting…) Basic Objective –Comparative Analysis of Algorithms Implementation –Implemented engine in Java using JDK 1.4.2 –Apache Xerces 2.6.2 for parsing (both XML and XPath) –Used existing XSQ Java implementation –Benchmark for evaluation - XPathMark

3. XStream Builds parse tree for input query Maintains an event stack Keeps matching input streaming document for each node

4. Our Contributions Correction – Verification – Performance Figures – Recursive Query Handling – Query Evaluation Support –

5. Performance Benchmark: XPathMark, set of 23 queries (mostly predicate queries) Criteria: Queries Per Second Rate Test Setup: Run on elaine2, 900 MHz 2-CPU processor Results: –XSQ QPS: 4.39Coverage: 17% –TurboXPath QPS: 5.75 Coverage: 21%+ Time = XML Parsing + Processing QPS: XStream 30% faster + better coverage on given benchmark

6. Recursive Query Handling For query node n and elements e1, e2 in d –Both e1 and e2 match n –e1 contains e2 Example: Document Query //a/b FA-based algorithms –Exponential number of states

7. Query Evaluation Support 2 Questions: –Filtering Does this document match the query? F1: XML => boolean –Evaluation What parts of the document match the query? F2: XML => XML Modifications: –Output buffers for predicate owner –Predicate node buffers –Predicate evaluation

8. Multiple Simultaneous Queries combine the queries OR-ing them together: q = (q 1 ) | (q 2 ) | … | (q n ); Resulting query has multiple output nodes Associate a query-id with output node

9. Conclusion Streaming XPath Engine –All Objectives met! (XPath Stream Evaluator implemented, Performance Analysis) –Algorithm correction and enhancements Future Directions –Backward Axis Support –Function Support – reuse predicate evaluation model –Extended expression type support –Predicate Pipelining