DBMS Mappings

Mappings

Process of transforming request and results between three level it's called mapping.

There are the two types of mappings:

  1. Conceptual/Internal Mapping
  2. External/Conceptual Mapping

1. Conceptual/Internal Mapping:

  • The conceptual/internal mapping defines the correspondence between the conceptual view and the store database.
  • It specifies how conceptual record and fields are represented at the internal level.
  • It relates conceptual schema with internal schema.
  • If structure of the store database is changed.
  • If changed is made to the storage structure definition-then the conceptual/internal mapping must be changed accordingly, so that the conceptual schema can remain invariant.
  • There could be one mapping between conceptual and internal levels.

2. External/Conceptual Mapping:

  • The external/conceptual mapping defines the correspondence between a particular external view and conceptual view.
  • It relates each external schema with conceptual schema.
  • The differences that can exist between these two levels are analogous to those that can exist between the conceptual view and the stored database.
  • Example: fields can have different data types; fields and record name can be changed; several conceptual fields can be combined into a single external field.
  • Any number of external views can exist at the same time; any number of users can share a given external view: different external views can overlap.
  • There could be several mapping between external and conceptual levels.


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Database System Architecture