Relaxing Join and Selection Queries

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Relaxing Join and Selection Queries

• Rares Vernica
• UC Irvine, USA
• Joint work with Nick Koudas, Chen Li, and Anthony
  K. H. Tung

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Query Example

• SELECT FROM Jobs J, Candidates C
• WHERE J.Salary
• AND J.Zipcode C.Zipcode
• AND C.WorkExp 5

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What if the query answer is empty?

• SELECT FROM Jobs J, Candidates C
• WHERE J.Salary
• AND J.Zipcode C.Zipcode
• AND C.WorkExp 5

• Adjust the conditions
• What conditions to adjust?
• How to adjust them?

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Example Percentages of Empty Result Queries

• In a Customer Relationship Management (CRM)
  application developed by IBM
  
• 18.07 (3,396 empty result queries in 18,793
  queries)
  
• In a real estate application developed by IBM
• 5.75
• In a digital library application JCM00
• 10.53
• In a bioinformatics application RCP98
• 38
• Efficient Detection of Empty-Result Queries
  (p.1015)Gang Luo (IBM T.J. Watson Research
  Center, USA) VLDB 2006

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Observations

• Different ways to adjust the conditions Select
  vs. Join
  
• How much to adjust each condition?Salary vs. Salary
• Adjust join vs. Adjust both selections

Salary
WorkExp 5
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Contributions

• Query relaxation framework for selections and
  joins
  
• Lattice-based approach for query relaxation
• Efficient relaxation algorithms

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Overview

• Motivation
• Query Relaxation
• Lattice-based Relaxation
• Relaxation Algorithms
• Variations
• Experiments

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Query Relaxation

• Top-k / Nearest neighbor
• Weight for each condition
• Skyline
• No weights are needed
• Conditions are not considered equal
• Return non dominated points

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Query Relaxation

• Skyline
• Stephan Börzsönyi, Donald Kossmann, Konrad
  Stocker The Skyline Operator. ICDE 2001

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Overview

• Motivation
• Query Relaxation
• Lattice-based Relaxation
• Relaxation Algorithms
• Variations
• Experiments

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Lattice-based Relaxation
R select on Jobs J join condition S select
on Candidates
Salary WorkExp 5
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Overview

• Motivation
• Query Relaxation
• Lattice-based Relaxation
• Relaxation Algorithms
• Variations
• Experiments

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Relaxing Selection Conditions
INCORRECT

• Algorithm
• Compute Skyline on Jobs
• Compute Skyline on Candidates
• Join the Skylines

Salary
WorkExp 5
Empty Join
Skyline
Skyline
Skyline
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Relaxing Selection Conditions

• Join First Algorithm
• Compute the join(disregarding the selections)
• Compute Skyline on join results

Salary
WorkExp 5
Join
Skyline
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Relaxing Selection Condition

• Variations
• Pruning Join
• Build the Skyline during the join
• Pruning Join
• Pruning Join
• Build the local Skyline before the join
• Sorted Access Join
• Fagins Top-k sort the columns on relaxation
• Compute the join Skyline

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Relaxing all conditions

• Multi-Dim.-Index-based-Relaxation Algorithm
• Traverse the index structure top-down
• Form pairs of nodes or records
• Build the Skyline

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Overview

• Motivation
• Query Relaxation
• Lattice-based Relaxation
• Relaxation Algorithms
• Variations
• Experiments

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Variations

• Computing Top-k over Skyline
• Weight to each condition
• Queries with multiple joins
• Conditions on nonnumeric attributes
• Dominance checking function

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Overview

• Motivation
• Query Relaxation
• Lattice-based Relaxation
• Relaxation Algorithms
• Variations
• Experiments

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Experimental Setting

• Datasets
• Real
• Internet Movie Database (IMDB)
• Movies (120k) ActorInMovies (1.2m)
• Census-Income UCI KDD Repository
• Census (200k)
• Synthetic
• Independent, Correlated, and Anticorrelated
• Implementation
• GNU C
• Spatial Index Library (R-tree)
• Linux, AMD Opteron 240, 1GB RAM

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Different algorithms, different behaviors
IMDB Dataset
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Different datasets, different behaviors
Anticorrelated Dataset
Correlated Dataset
Independent Dataset
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How big is the Skyline?
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Relaxing join takes time
Self-join on Census Dataset
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Top-k over Skyline
IMDB Dataset
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Related Work

• Muslea et al.
• Alternate forms of conjunctive expressions
• Efficient Skyline algorithms
• Selection queries
• Efficient Top-k algorithms
• Require weights for conditions

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Conclusions

• Query relaxation framework for selections and
  joins
  
• Lattice-based approach for query relaxation
• Efficient relaxation algorithms

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Future Work

• Optimum use of the lattice structure
• Relax conditions on string attributes
• Algorithms applicable outside the databases

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Questions ?
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(No Transcript)
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Skyline vs. Top-k
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Skyline vs. Top-k over Skyline