Index Classification (Contd.)

• Dense vs. Sparse: If there is at least one data entry per search key value (in some data record), then dense.

  • Alternative 1 always leads to dense index.
  • Every sparse index is clustered!
  • Sparse indexes are smaller;

Ashby, 25, 3000

Smith, 44, 3000

Ashby

Cass

Smith

22

25

30

40

44

44

50

Sparse Index

on

Name

Data File

Dense Index

on

Age

33

Bristow, 30, 2007

Basu, 33, 4003

Cass, 50, 5004

Tracy, 44, 5004

Daniels, 22, 6003

Jones, 40, 6003

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