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Indexing OLAP Data: Join Indices

  • Join index: JI(R-id, S-id) where R (R-id, …) join S (S-id, …)
  • Traditional indices map the values to a list of record ids
    • It materializes relational join in JI file and speeds up relational join
  • In data warehouses, join index relates the values of the dimensions of a start schema to rows in the fact table.
    • E.g. fact table: Sales and two dimensions city and product
      • A join index on city maintains for each distinct city a list of R-IDs of the tuples recording the Sales in the city
    • Join indices can span multiple dimensions

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