MiniCon: A Scalable Algorithm for Answering Queries Using Views

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MiniCon A Scalable Algorithm for Answering
Queries Using Views

• Rachel Pottinger and Alon Levy
• Affiliates Meeting
• February 24, 2000

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Answering Queries Using Views

• Problem access views (stored queries) instead of
  original relations
• Useful in data integration and query optimization
• NP-Complete
• Many papers on the subject
• No empirical testing of algorithms

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Data Integration
Cheap.com -Prices of cars Cheap(price) -
Cost(model,price)
Car Sale Information
Used.com -Prices and years of used
cars Used(price, year) - Cost(model, price)
Age(model,year)
Query What price do cars made in 1996 sell
for? Query(Price, 1996)- Cost(Model,Price)
Age(Model, 1996)
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View challenges

• Data sources (Cheap.com, Used.com) are
  pre-calculated views
• Views are not complete
• Get the most answers possible given the views
• Many data sources

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Inverse Rules

• Take the views and invert themCheap(price)-
  Cost(car,price) ?Cost(?,price) -
  Cheap(price)
• Now can query on database relations to find all
  relevant rules
• Run regular database functions to find answers
• Extended to be more efficient in our paper

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Bucket Algorithm Populating buckets

• For each relation in the query, place relevant
  views in the relations bucket
• Inputs
• Query(Price,1996)-Cost(Model,Price)
  Age(Model,1996)
• Cheap(price)-Cost(model,price)
• Used(price,year)-Cost(model,price)
  Age(model,year)

Buckets
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Combining Buckets

• For every combination in the Cartesian products
  from the buckets, check containment in the query

• Candidate rewritings
• Query1(x) - Cheap(Price)
• Used(_, 1996) ?
• Query2(x) - Used(Price,_)
• Used(_, 1996) ?

Bucket Algorithm will check all possible
combinations
Buckets
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The MiniCon Algorithm

• Concentrate on variables rather than relations to
  create MiniCon Descriptions (MCDs)
• Combine MCDs that only overlap on returned view
  variables

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MiniCon Description Formation

• Form all MiniCon Descriptions (MCDs) that map all
  query variables that have to be mapped together
• Inputs
• Query(Price,1996)- Cost(Model,Price)
  Age(Model,1996)
• Cheap(price)-Cost(model,price)
• Used(price,year)-Cost(model,price)
  Age(model,year)

view
mapping
relations mapped
Used Model?model, 1, 2
Price?price, 1996?year
MCDs
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MiniCon Combination

• Take all combinations of MCDs that
• map disjoint sets of relations
• map all relations of the query
• MCDs

view
mapping
relations mapped
Used Model?model, 1, 2
Price?price, 1996?year
Rewriting Query(Price,1996)-Used(Price,
1996)
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Experimental resultsMany rewritings
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Experimental ResultsFew rewritings
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See paper for details

• Including
• Further experimental evaluation
• Extension to handle interpreted predicates
• Improvement to Inverse Rules
• Query optimization extension