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Schemas

19 October, 2015 - 10:14

A schema is an overall description of a database and it is usually represented by the Entity Relationship diagram. There are multiple subschemas which are representations of the external models. To put it into perspective of one database:

  • External Schemas :
  • multiple multiple subschemas = multiple external views of the data •
  • Conceptual Schema : one only
  • Data items, relationships & constraints – ER diagram
  • Physical Schema : one only
  • Record definitions, representation methods
  • Access methods, indexes, hashing