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Hippo

Hippo. a System for Computing Consistent Query Answers to a Class of SQL Queries. Motivation - Inconsistent data. Enforcing data consistency no longer applicable: Data Integration – Consistent data sources, but inconsistent global view. Long-running transactions. Efficiency reasons.

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Hippo

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  1. Hippo a System for Computing Consistent Query Answersto a Class of SQL Queries

  2. Motivation - Inconsistent data Enforcing data consistency no longer applicable: • Data Integration – Consistent data sources, but inconsistent global view. • Long-running transactions. • Efficiency reasons.

  3. Consistent Query Answers Repair • Instance satisfying the constraint. • The set of changes is minimal. There can be an exponential number of repairs. Tuple t is a consistent answer to Q if t is an answer to Q in every repair.

  4. Computing CQA • Query rewriting For query Q construct Q’ which evaluation returns consistent answers of Q. • Logic programming Use disjunctive program to specify repairs and query result. • Condensed representations of repairs

  5. Conflict Hypergraphs • Vertex – database tuple • Edge – conflicting tuples (J.S.,BUF) (J.S.,CHO) (D.G.,BUF) (M.A.,BUF) (M.A.,CHO) Repair – Maximal Independent Set (M.A.,NYC)

  6. Hippo – System Description • Conflict hypergraph – stored in RAM • Denial integrity constraints • Queries: • SQL frontend – RDMBS independent • Platform independent (Java2)

  7. Hippo is fast • Selection and Join – as fast as underlying database system. (QR takes approx. twice the time) • Union and Difference – takes approx. Twice the time of simple query evaluation. (QR the same for difference).

  8. Future Work • Projection • In general problem is co-NP-data-complete. • Find an efficient heuristic. • Characterize hypergraphs where projection is easy • Preferences • User provides preferences on resolving conflicts. • Computing Preferred CQA still easy.

  9. References • M. Arenas, L. Bertossi, J. Chomicki. Consistent Query Answers in Inconsistent Databases. PODS’99 • J. Chomicki, J. Marcinkowski. Minimal Change Integrity Maintenance using Tuple Deletions. Under revision for Information and Computation. • J. Chomicki, J. Marcinkowski, S. Staworko. Computing Consistent Query Answers using Conflict Hypergraphs. Under conference submission. • http://www.cse.buffalo.edu/~chomicki

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