Maintaining XPath Views in Loosely Coupled Systems

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Maintaining XPath Views in Loosely Coupled Systems
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Motivation
Base Data (BD)
Base Data
View Result
View Result
View Maintenance

• Our goal is an XML caching system for the WWW.
• Our focus is on keeping the cache up-to-date
  (i.e. maintaining the materialized views)

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Incremental XML View Maintenance

• Incremental Maintenance of Path Expression Views.
  Arsany Sawires et al. SIGMOD 2005
• Incremental Maintenance for Materialized
  XPath/XSLT Views. Makoto Onizuka et al. WWW 2005
  
• Incremental Evaluation of a monotone XPath
  Fragment. Hidetaka Matsumura et al. CIKM 2005
• Order-Sensitive View Maintenance of Materialized
  XQuery Views. Katica Dimitrova et al. ER 2003
• And others

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The Goal of this Paper
Base Data
View Result
View Maintenance

• All solutions so far assumed tight coupling. Good
  for same-system scenarios.
• Our target WWW caching system requires a loosely
  coupled XPath view maintenance solution.

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The Rest of This Talk
Outline
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Data and Query Model
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Tight Coupling Assumptions
Update Path node idsand intermediate results
Queries with node ids as context
Base Data (BD)
View Result (VR)
Results includenode ids
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Loose Coupling Assumptions
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Overview on the Approach
Input U, V, VR
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Updates and Their Effects

• Add

• Base Updates

, Delete, or Modify

• How could a base addition U affect VR ?

Internal
External
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IRrelevance Test (IRT)
Res(V) D1 , D2 ResD(U) D2
Intersection ----(1)
HOW ?
Embedding -----(2)
OK
IF ? node on Spine(U), either (1) or (2) does not
hold,Then the IRT is PositiveElse it is
Negative.
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Intensional XPath Intersection

• Def. ?1 n ?2 iff ? a hypothetical BD s.t.
  Res(?1) n Res(?2) is not empty.

Spine(?1) n Spine(?2)
?1 n ?2
On the Intersection of XPath Expressions.Beda
Hammerschmidt et al. IDEAS 2005
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Self Maintainability Test (SMT)

• Write a correct SM Expression over VR.
• Correct No less and No more than U.

• No less ? OK
• No more ? ?

Res(V) ? Res(PrefD (U))
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Intensional XPath Containment

• Def. ?1 ? ?2 iff ? hypothetical BD, Res(?1) ?
  Res(?2)

Containment and Equivalence for a Fragment of
XPath.Gerome Miklau and Dan Suciu. JACM 2004
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A Quick Recap
- XPath Intersection- XPath Embedding
IRT
N
SMT
- XPath Containment

• Updates Addition Deletion Modification

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Experiments

• No false positives ? perfect precision.
• How about the recall (effect of false negatives)?

XMARK (100MB) - XPath generator (YFilter)
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Exp.1 Varying the Number of Views
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Exp.2 Varying Parameters of U
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Conclusion Discussion

• We have pointed out the need for loose coupling
  in XML View Maintenance.
• We have taken a first-step in this direction
  using intensional XPath intersection and
  containment tests.
• Looking Forward
• Extend the View and Update Language.
• Exploit schema information, if available.
• Handle order predicates, e.g. Book2.
• Thanks For Listening