VLDB 2006, Sept 14, Seoul, Korea

Arsany Sawires UC Santa Barbara

Junichi Tatemura NEC Labs

Oliver Po NEC Labs

Divyakant Agrawal NEC Labs

Amr El Abbadi UC Santa Barbara

K. Selcuk Candan NEC Labs

Maintaining XPath Views in Loosely Coupled Systems

View Result

View Maintenance

Base Data(BD)

Motivation

• 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)

Base DataView Result

Update

User Queries

Incremental XML View MaintenanceIncremental 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 …

View Maintenance

The Goal of this Paper

• 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.

Base DataView Result

Update

The Rest of This Talk

Model

Is it Really Effective?

Conclusion

END

Tight Coupling

Loose Coupling Approach

Outline

A1

B1

C

1

E1

D

1X1 Y1

M1

BD

A2

B2

C2

D

2X2 Y2

Z2

A3

B3

D

3X3

Data and Query Model

D

1X1 Y1

D

2X2 Y2

Z2

C

C3

Update U

M

BD

AB

View V

A

BD

B

CD

View Result VR

Tight Coupling Assumptions

Update Path: node idsand intermediate results

Base Data(BD)

View Result(VR)

Results includenode ids

UpdateQueries with node ids as context

Loose Coupling Assumptions

C

View V

A

BD

B

CD

Update U

M

BD

AB

View Result VR

D

X Y

D

X Y

Z

Overview on the Approach

Input U, V, VR

Update VRP

N

SMTSelf Maintainability Test

Re-compute VR

N

Ignore U P IRTIRrelevance Test

Updates and Their Effects

Add

• How could a base addition U affect VR ?

• Base Updates: , Delete, or Modify

Internal External

Explicit Implicit

D

2

A1

B1

C

1

E1

Y2

D

1Y1

T1

A

B

E

D

TY

IRrelevance Test (IRT)

A

B

C

D

Res(V) = { D1 , D2 }

ResD(U) = { D2 }

Intersection ----(1)

Embedding -----(2)

IF node on Spine(U), either (1) or (2) does not hold,Then the IRT is PositiveElse it is Negative.

D

1Y1

D

2Y2T1

HOW ?

OK

Intensional XPath IntersectionDef. 1 ∩ 2 iff a hypothetical BD s.t.

Res(1) ∩ Res(2) is not empty.

Spine(1) ∩ Spine(2)

L

A

B

C

A

D

*E

N

L

1 ∩ 2

A B C*

*A D E

M

On the Intersection of XPath Expressions.Beda Hammerschmidt et al. IDEAS 2005

Self Maintainability Test (SMT)• Write a correct SM Expression over VR.

• Correct ≡ No less and No more than U.

• No less OK

• No more ?E1

D

2

A1

B1

C

1

Y2

D

1Y1

T1

A

B

C

D D

1Y1

D

2Y2T1

A

B

E

D

TY

SME

Res(V) Res(PrefD (U))

Intensional XPath Containment

A

B

C

D

A

B

E

D

Def. 1 2 iff hypothetical BD,

Res(1) Res(2)

Homomorphism ?

Containment and Equivalence for a Fragment of XPath.Gerome Miklau and Dan Suciu. JACM 2004

A Quick Recap

Update VRP

N

SMT - XPath Containment

Ignore U P IRT- XPath Intersection- XPath Embedding

• Updates: Addition – Deletion – Modification

Internal Explicit Implicit

Experiments

XMARK (100MB) - XPath generator (YFilter)

ivesFalseNegatPositives

Positives

Rel. Saving =

• No false positives perfect precision.

• How about the recall (effect of false negatives)?

Exp.1: Varying the Number of Views

0

0.2

0.4

0.6

0.8

1

1.2

10 20 30 40 50 60 70 80 90 100

Number of views

Rel

. sa

ving

Base Additions

Base Deletions

Exp.2: Varying Parameters of U

0

0.2

0.4

0.6

0.8

1

1.2

0 0.2 0.4 0.6 0.8 1

Probability of "//"

Rel

. sa

ving

Base AdditionsBase Deletions

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. Book[2].

Thanks For Listening