Logical data independence

Logical data independence

• Encapsulation
  • Private portion can be changed
  • Hiding: public / private components
  • Mapping: between private / public components
  • Methods and encapsulation often bypassed by query languages

• Virtual data
  • “Relational view”
  • Useful e.g. when changing the schema
  • Update problem…
  • Relational views:
    • mapping but not hiding
  • OO systems:
    • hiding, but weak mapping

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