Reference Work Entry

Encyclopedia of Database Systems

pp 2680-2681

Sparse Index

  • Mirella M. MoroAffiliated withFederal University of Rio Grande do Sul
  • , Vassilis J. TsotrasAffiliated withUniversity of California-Riverside


Non-dense Index


Consider a tree-based index on some numeric attribute A of a relation R. If an index record (of the form <search-key, pointer>) is created for some of the values that appear in attribute A, then this index is sparse.

Key Points

Tree-based indices are built on numeric attributes and maintain an order among the indexed search-key values. Hence, they provide efficient access to the records of a relation by attribute value. Consider for example an index built on attribute A of relation R. The leaf pages of the index contain index-records of the form <search-key, pointer>, where search-key corresponds to a value from the indexed attribute A and pointer points to the respective record in the indexed relation R with that attribute value. If not all distinct values that appear in R.A also appear in index records, this index is sparse, otherwise it is called dense.

A sparse index needs a way to access even the relation records with value ...

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