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MySQL + SQL · Lesson 9

Database Architecture and Three-Schema Architecture

Three-Schema Architecture

DBMS uses a three-level (three-schema) architecture to separate the user's view from physical storage. This separation gives data independence.

The Three Levels

LevelAlso CalledDescribes
ExternalView levelWhat each user sees (custom views)
ConceptualLogical levelWhole database structure: tables, relationships
InternalPhysical levelHow data is physically stored on disk

Main Components of DBMS

  • Query processor — understands and runs SQL.
  • Storage manager — handles files, indexes and buffers.
  • Transaction manager — ensures ACID properties.
  • Data dictionary (catalog) — stores metadata.

Summary

  • Three levels: external (view), conceptual (logical), internal (physical).
  • Components: query processor, storage manager, transaction manager, data dictionary.
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