1. High-Performance XML Filtering with YFilter
Publish-Suscribe-System
to filter XML-Streams
used in SDI-Systems

2. Problem of XFilter filtering large numbers of query specifications
(separate Finite State Machine for each query)
YFilter uses an Nondeterministic Finite
Automaton (NFA)
- exploit commonality among path queries
- combine all queries in a single machine

3. Constructing a combined NFA
Four basic locations steps in XPath are
„/a“
„//a“
„/*“
„//*“
Construct NFA fragments for these steps
and combine them

4. NFA fragments of the four basic locations steps
/* :
//* : * a * * *

5. * * * * * * * Combining NFA Fragments a a a b b b b a a b b b b
Important Note: new queries can be easily be added to an existing system

6. Q1=/a/b Q2=/a/c Q3=/a/b/c Q4=/a//b/c Q5=/a/*/c Q6=/a//c Q7=/a/*/*/c
NFA Example
Q1=/a/b
Q2=/a/c
Q3=/a/b/c
Q4=/a//b/c
Q5=/a/*/c
Q6=/a//c
Q7=/a/*/*/c
Q8=/a/b/c

7. Some Comments on Efficiency
reduction in machine size
path-sharing
easy adding of new queries

8. Implementation Creating a data structure for each state with
ID of the state
type information
hash table for transitions [symbol | ID]
for accepting states, ID list of queries

9. NFA Implementation

10. Execution -start of Document -start of Element -end of Element
Execution in an event-driven fashion
Run-time stack for backtracking
-start of Document
-start of Element
-end of Element
Important Note: NFA execution until all potential accepting states
have been reached

12. - value-based predicates - nested-path Methods:
Predicate Evalution
- value-based predicates
- nested-path
Methods:
Inline
Selection Postponed (SP)

13. Performance Results YFilter faster than XFilter and the hybrid
approach
Cost and machine size affords are small
For value-based predicates, the SP approach was found to perform much better than the Inline approach

14. Performance Test Multi-query processing time (MQPT) in ms
Number of Queries (x1000)

15. Conclusions YFilter provides high-performance XML Filtering
Dominant costs for document parsing and
result collection