Streaming XPath Engine

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 4.39 Coverage 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 ltagtltagtltb/gtlt/agtltbgtlt/bgtlt/agt
• 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 gt boolean
• Evaluation
• What parts of the document match the query?
• F2 XML gt XML
• Modifications
• Output buffers for predicate owner
• Predicate node buffers
• Predicate evaluation

8
Multiple Simultaneous Queries

• combine the queries OR-ing them together
• q (q1) (q2) (qn)
• 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