Download Query Relaxation Using Malleable Schemas

Query Relaxation Using
Malleable Schemas
Xuan Zhou, Julien Gaugaz, Wolf-Tilo Balke, Wolfgang Nejdl
L3S Research Center
Leibniz University
Hanover, Germany
Presented by Aaron Stewart
BYU CS 652
Spring 2009
Problem
+
=?
Problem
• Multiple data sources
• Unmatched schemas
Approach
1. Malleable schemas
2. Discover correlations
3. Relax user queries
Malleable Schemas
• Allow duplicate fields
• Allow related fields
Malleable Schemas
Malleable Schemas
first_name,
sur_name
name
Malleable Schemas
body
contents
In Practice: Tables
• “…a malleable schema… contains
imprecise and overlapping definitions of
attributes or relationships.”
• “In this way, a malleable schema can
capture such heterogeneous data
structures as in Figure 1.”
In Practice: Tables
In Practice: Tables
Attributes (database fields, columns)
Entities (database records, rows)
Equivalently: Distinct tables
Query Relaxation Planning
• Multiple queries
– Different columns or tables
– As few queries as possible
• Exponential number of relaxed queries
– Evaluate in order of precision
– Stop at k results
Query Relaxation Planning
relaxed attribute
child attributes
A1
A2
Query Relaxation Planning
• A “relaxed query always yields better
precision than its child queries, so that it
should always be evaluated prior to its
child queries”
Parent/Child Relationship
• We would think A is the parent, and A1
and A2 are the children, but…
• Put them in order of correlation probability
– If P(A|A1) > P(A|A2)
– Then A => A1 => A2
Query Relaxation Planning
Query Relaxation
Experiments
• Data sets
– IMDB Movies
– Amazon.com DVDs and VHS videos
Results
Results
Results
Analysis
• Strengths
– Handles mixed schemas
– Well-designed algorithms (IMO)
• Future work
– Speed